Let's look at the most obvious reasons most research point out right off the bat:

Critical age for mastering

Have you ever thought about the critical age for absorbing a new language by a kid? We hear all quite often that kids are ‘sponges’ who remember the words at once without any extra efforts at all. Recent researches prove that even babies less than a year old that grow up in bilingual environment, show better results in their native language and start reading earlier. At the age of 7 or 8 children can soak up every word without an accent and with fluent grammar. Thus after this critical period the ability to learn a second language steadily declines and post-puberty our capacity for foreign language attainment is reduced significantly.

What are the main benefits for your bilingual kid in future?

Nearly 1.5 billion people around the world speak English and this number is rising steadily every year. Beyond that, more than half of the world’s population speaks more than one language on a regular basis. Obviously, speaking two or more languages has practical benefits in progressively globalized world. Nevertheless nowadays economic and geopolitical changes draw also our attention to such languages as Arabic, Chinese, Korean, Portuguese, Spanish, Japanese or Russian. Besides, students tend to study European languages with the idea that being multilingual puts them at an obvious advantage on the world market.

Being multilingual helps young people to appreciate different cultures through learning their language. It encourages them to dig deeper, realize the impact of great cultures and develop greater tolerance for different ways of being in the world. It goes without saying, learning a foreign language is a part of most school and colleague programs. Furthermore most undergraduate programs and postgraduate courses have foreign language classes. According to a 2014 Coalition for International Education study 30% of U.S. business executives missed opportunities abroad due to a lack of on-staff language skills, and nearly 40% reported that they had failed to reach their international potential due to language barriers.

And what about brains?

Returning to the present time, researchers show us today impressive results exploring cognitive system of monolinguals and bilinguals. Astonishingly…it grows kids’ brains. It helps to grow certain brain sections and to slow brain aging. Those who keep up proficiency in language learning achieve better results in standardized math, vocabulary tests, reading and have better listening skills being more perceptive of non-standard points of view. Bilingualism forces the brain to resolve mental internal conflict providing the mind with a certain workout that enhances its cognitive muscles. Even thinking in a foreign language reduces preconceived notions in our decision-making. Bilinguals tend to make more rational decisions as some biases of a foreign language can subconsciously influence your judgment and bilinguals are more confident with their choices after thinking it over in the second language and concluding whether their previous opinions are still correct. Also according to a Spain’s University of Pompeu Fabra study bilinguals are more adept at focusing on relevant information and editing out the irrelevant. They are better at observing their surroundings and spotting misleading information. In 2014 Thomas Bak at the University of Edinburgh (at a sample of 850 older people) revealed that those who had learned a second language in later childhood, showed better results in IQ test in comparison to predicted results according to their IQ test scores at the age of 11. Bak also has found that bilingual patients develop dementia 4 to 5 years later than monolinguals.

Infants and bilingual input

Newborn babies evolving in bilingual families learn two languages concurrently without any intermingling or tardiness. Though it is unclear how infants cope with an incoherent input, let’s survey current achieved results by researchers from Concordia University. Krista Byers-Heinlein reported in her research that infants and adults monitor and control their languages while real language listening. Thus infants use language-control mechanisms to predominantly activate the currently heard language during just listening. Also bilingual babies increase cognitive load during language switches. According to a Pennsylvania State University study, the “juggling” skill makes children great multitaskers, because they can easily switch between different structures. Also Agnes Melinda Kovacs and Jacques Mehler proved in another 2009 Harvard study that 7-month-old infants, raised with 2 languages from birth, show improved cognitive control abilities in comparison to monolingual babies. This research also shed light on previous debates regarding pros and cons of influence to a bilingual input. The research proved an advantage in executive control for bilingual infants either in visual or auditory signals. The exposure of crib bilingualism stimulates the development of significant cognitive control mechanisms at a non-verbal age. Bilingual children showed better skills in tracking changes in their environment.

Bottom line

Thus, we can infer that learning a second language in childhood provide cognitive advantages across our lifelong education. Despite all aforementioned advantages for your kid’s future career, bilingualism comprises even more fundamental gain than just communication with a wider range of people. It can make you smarter and in better mental health.