There is no manual nutritional information or spices on how to teach your child to be smart but there exist a scientific principles that will surely do the job for you if you follow it more closely. Only if modern busy schedule doesn't steal quality time away needed for their child to grow intellectually and healthily.
To enhance the 3 major domain of your child: the cognitive, psychomotor and affective domain. Here is what to do by parents, guidance and teachers which is backed up by long scientific research :

1. Do teach social skills.

A 20-year Study by researchers at Pennsylvania State and Duke University shows a positive correlation between children's social skills in kindergarten and their success in early adulthood. Teaching your kids how to resolve issues with friends, share their belongings, listen without interrupting, and help others in the home is a great place to start.

2. Don't overprotect.

In today's age of helicopter parenting, many parents (including myself) have difficulty allowing our kids to solve problems, but rather rush to fix challenges for them.

Drawing on a Harvard University study, Julie Lythcott-Haims argues that allowing kids to make mistakes and develop resilience and resourcefulness is critical in setting them up for success.

Newsflash: This isn't easy. We all need to walk a fine line between protecting our children and letting them tackle problems in order to learn from them.

3. Do get your kids involved in academics early (then encourage independence when they are older.

Research shows that reading to your children and teaching them math early can greatly impact achievement in later years. However, it is best to start weaning kids off homework help later in elementary school, as helping your child with homework can actually stunt their development.

Parents should always communicate interest in their children's schooling, but encourage them to take charge of their work independently.

4. Don't let them languish in front of a screen.

Too much screen time has been linked to childhood obesity, irregular sleep patterns, and behavioral issues. In addition, a 2017 study by Greg L. West at the University of Montreal revealed that playing "shooter" games can damage the brain, causing it to lose cells.

So what can we do about the ever-so-helpful digital babysitter that so many of us rely on?

According to the American Academy of Pediatrics, entertainment "screen time" should be limited to two hours a day.

Another helpful idea: encourage your children to become content creators rather than passive consumers. Encourage them to learn computer programming, 3D modeling, or digital music production and turn screen time into a productive endeavor.

5. Do set high expectations.

Harnessing data from a national survey, a UCLA team discovered that the expectations parents hold for their kids have a huge effect on achievement.

The study found that, by the time they were four, almost all the children in the highest performing study group had parents who expected them to attain a college degree.

6. Don't spend too much time praising innate qualities such as intelligence or looks.

"Wow, you got an A without even studying? You are so smart!"

A Stanford University study shows that praising children with statements like the above and focusing on their intelligence, can actually lead to underperformance.

As an alternative parenting strategy, parents are encouraged to offer praise that focuses on the effort kids expend to overcome problems and challenges by demonstrating grit, persistence, and determination.

7. Do assign chores.

There is a significant body of evidence that shows that chores are beneficial for childhood development. Yet, in a Braun Research poll, just 28 percent of parents said they regularly assign chores to their kids.

A University of Minnesota analysis of data found that the best predictor of success in young adulthood was whether children had performed chores as young as three or four.

8. Don't tune out.

According to a survey by Common Sense Media, 28 percent of teens said their parents were addicted to their mobile devices. Another recent study by AVG discovered that 32 percent of children surveyed felt unimportant when their parents were distracted by their phones.

As the first generation of parents with 24/7 access to the Internet, it is important for us to know when to disconnect and focus on the family.

9. Do strive for a peaceful, loving home

Children in high-conflict families tend to fare worse than children of parents that get along, according to a University of Illinois study review. Creating a loving, supportive environment is a staple of healthy, productive offspring.

If you do have an argument with a spouse, it is recommended to model fair fighting, boundary-setting, and a focus on reconciliation and resolution.

10. Don't be too hard (or too soft)

Diana Baumrind, in her groundbreaking 1966 study, distinguished between authoritarian (very strict), permissive (very lenient), and authoritative (equally disciplined and loving) parents.

In short, authoritarian parents are too hard, permissive parents are too soft, and authoritative are just right.

When a child models their authoritative parents, they learn emotion regulation skills and social understanding that are critical for success.

10 other ways to make your kids smarter: Steps Backed By Science research.

1) Music Lessons
Plain and simple: research show music lessons make kids smarter :

Compared with children in the control groups, children in the music groups exhibited greater increases in full-scale IQ . The effect was relatively small, but it generalized across IQ subtests, index scores, and a standardized measure of academic achievement.
In fact musical training helps everyone,
young and old :

A growing body of research finds musical training gives students learning advantages in the classroom. Now a Northwestern University study finds musical training can benefit Grandma, too, by offsetting some of the deleterious effects of aging.

2) Don’t Read To Your Kids, Read With Them
Got a little one who is learning to read? Don’t let them just stare at the pictures in a book while you do all the reading.
Call attention to the words. Read with them, not to them. Research shows it helps build their reading skills:

When  shared book reading is enriched with explicit attention to the development of children’s reading skills and strategies, then shared book reading is an effective vehicle for promoting the early literacy ability even of disadvantaged children.

3)Sleep Deprivation Makes Kids Stupid
Missing an hour of sleep turns a sixth grader’s brain into that of a fourth grader.

“A loss of one hour of sleep is equivalent to [the loss of] two years of cognitive maturation and development,” Sadeh explained.
There is a correlation between grades and average amount of sleep.

Teens who received A’s averaged about fifteen more minutes sleep than the B students, who in turn averaged fifteen more minutes than the C’s, and so on. Wahlstrom’s data was an almost perfect replication of results from an earlier study of over 3,000 Rhode Island high schoolers by Brown’s Carskadon. Certainly, these are averages, but the consistency of the two studies stands out. Every fifteen minutes counts.

4)IQ Isn’t Worth Much Without Self-Discipline

Self-discipline beats IQ at predicting who will be successful in life.

Dozens of studies show that willpower is the single most important keystone habit for individual success… Students who exerted high levels of willpower were more likely to earn higher grades in their classes and gain admission into more selective schools. They had fewer absences and spent less time watching television and more hours on homework.

“Highly self-disciplined adolescents outperformed their more impulsive peers on every academic-performance variable,” the researchers wrote. “Self-discipline predicted academic performance more robustly than did IQ. Self-discipline also predicted which students would improve their grades over the course of the school year, whereas IQ did not.… Self-discipline has a bigger effect on academic performance than does intellectual talent.”

Grades have more to do with
conscientiousness than raw smarts.

…conscientiousness was the trait that best predicted workplace success. What intrigues Roberts about conscientiousness is that it predicts so many outcomes that go far beyond the workplace. People high in conscientiousness get better grades in school and college; they commit fewer crimes; and they stay married longer.

They live longer – and not just because they smoke and drink less. They have fewer strokes, lower blood pressure, and a lower incidence of Alzheimer’s disease.

Who does best in life? Kids with grit .

The best predictor of success, the researchers found, was the prospective cadets’ ratings on a noncognitive, nonphysical trait known as “grit”—defined as “perseverance and passion for long-term goals.”

5) Peer Group Matters
Your genetics and the genetics of your partner have a huge effect on your kids. But the way you raise your kids?
Not nearly as much.

On things like measures of intellectual ability and certain aspects of personality, the biological children are fairly similar to their parents. For the adopted kids, however, the results are downright strange. Their scores have nothing whatsoever in common with their adoptive parents: these children are no more similar in their personality or intellectual skills to the people who raised them, fed them, clothed them, read to them, taught them, and loved them for sixteen years than they are to any two adults taken at random off the street.
So what does have an enormous affect on your children’s behavior? Their peer group.

We usually only talk about peer pressure when it’s a negative but more often than not, it’s a positive.

Living in a nice neighborhood, going to solid schools and making sure your children hang out with good kids can make a huge difference.
What’s the easiest way for a college student to improve their GPA? Pick a smart roommate.

One study of Dartmouth College students by economist Bruce Sacerdote illustrates how powerful this influence is. He found that when students with low grade-point averages simply began rooming with higher-scoring students, their grade-point averages increased. These students, according to the researchers, “appeared to infect each other with good and bad study habits—such that a roommate with a high grade-point average would drag upward the G.P.A. of his lower-scoring roommate.”

6) Treats Can Be A Good Thing — At The Right Time
Overall, it would be better if kids ate healthy all the time. Research shows eating makes a difference in children’s grades :

Everybody knows you should eat breakfast the day of a big test. High-carb, high-fiber, slow-digesting foods like oatmeal are best, research shows. But what you eat a week in advance matters, too. When 16 college students were tested on attention and thinking speed, then fed a five-day high-fat, low-carb diet heavy on meat, eggs, cheese and cream and tested again, their performance declined.

There are always exceptions. No kid eats healthy all the time. But the irony is that kids often get “bad” foods at the wrong time.

Research shows caffeine and sugar can be brain boosters if it is used appropriately :
Caffeine and glucose can have beneficial effects on cognitive performance… Since these areas have been related to the sustained attention and working memory processes, results would suggest that combined caffeine and glucose could increase the efficiency of the attentional system.

They’re also potent rewards kids love.
So if kids are going to occasionally eat candy and soda maybe it’s better to give it to them while they study then when they’re relaxing.

7)Learning Is An Active Process
Research shows that for every hour per day children spent watching certain baby DVD’s and videos, the infants understood an average of six to eight fewer words than infants who did not watch them. Learning is an active process.

Real learning isn’t passive, it’s active.

Our brains evolved to learn by doing things, not by hearing about them. This is one of the reasons that, for a lot of skills, it’s much better to spend about two thirds of your time testing yourself on it rather than absorbing it. There’s a rule of two thirds. If you want to, say, memorize a passage, it’s better to spend 30 percent of your time reading it, and the other 70 percent of your time testing yourself on that knowledge.

8)Believe In Them
Believing your kid is smarter than average makes a difference.

When teachers were told certain kids were sharper, those kids did better — even though the kids were selected at random.

…Rosenthal and Lenore Jacobson (1968) did the same study in a classroom, telling elementary school teachers that they had certain students in their class who were “academic spurters.” In fact, these students were selected at random.

Absolutely nothing else was done by the researchers to single out these children.

Yet by the end of the school year, 30 percent of the the children arbitrarily named as spurters had gained an average of 22 IQ points, and almost all had gained at least 10 IQ points.

9) Striking balance between exercise, hobby and library.
spending more time on the field playing football or other sports activities or just catching fun than in the library doesn't make a child dumb or dull. Ensuring your child devotes time to both go along way to contribute to his or her intelligent quotient.

Being in good shape increases your ability to learn . After exercise people pick up new vocabulary words 20% faster.

Indeed, in a 2007 study of humans, German researchers found that people learn vocabulary words 20 percent faster following exercise than they did before exercise, and that the rate of learning correlated directly with levels of BDNF.

A 3 month exercise regimen increased bloodflow to the part of the brain focused on memory and learning by 30%.

In his study, Small put a group of volunteers on a three-month exercise regimen and then took pictures of their brains… What he saw was that the capillary volume in the memory area of the hippocampus increased by 30 percent, a truly remarkable change.

10)Happy Kids = Successful Kids
Happier kids are more likely to turn into successful, accomplished adults.

…happiness is a tremendous advantage in a world that emphasizes performance. On average, happy people are more successful than unhappy people at both work and love.

They get better performance reviews, have more prestigious jobs, and earn higher salaries. They are more likely to get married, and once married, they are more satisfied with their marriage.
And what’s the first step in creating happier kids? Being a happy parent .