Psychologists know that a young child can cope with many languages. If a child grows up in a situation where his mother speaks one language, his father another and yet another is spoken by his friends, the child will learn all three without a problem. Initially, the child may appear to be learning language slower than children who grow up in an environment where only one language is spoken, but by age 3 or 4, the child will speak all the languages of his environment as well as a child exposed to only one language. If the parents speak the mother tongue at home, and the child has the opportunity to speak English in other situations, then the child will learn both languages and not be disadvantaged in relationship to either of them.
“When a child learns two languages in his or her early years of life, a good foundation is laid for successful accomplishments in school and profession”
Baker refutes notions that acquiring two languages is detrimental to children, and makes it clear that children who learn two more more languages have significant and multiple advantages:
Parents, members of the public and politicians are sometimes prejudiced and believe that acquiring two languages from birth must be detrimental to a child’s language growth. In past times, it has been wrongly claimed that simultaneous acquisition will muddle the mind or retard language development. On the contrary, babies appear biologically ready to acquire, store and differentiate two or more languages from birth onwards. Infant bilingualism is normal and natural, with evidence that it is typically beneficial in many ways: cognitively, culturally, communicatively, for higher curriculum achievement, and to increase the chances of employment and promotion.
A study in the US showed that the children in Spanish-speaking households do not do better in school if their parents speak English to them at home. Not only that, they do better in Math if their parents speak Spanish at home. The explanation for this unexpected result is that the child is advantaged in cognitive development by speaking multiple languages and by speaking the mother tongue. This advantage is great enough that it more than overcomes the hurdle of learning Math in English.
Baker (2007) also notes that a child who speaks two languages learns a third language more easily than a monolingual child learns a second language. This finding underscores the benefits of learning more than one language for cognitive development and undermines old notions that too many languages results in interference with the child’s ability to learn language.
These facts call into question the ideas of some parents who may think that speaking English, rather than their mother tongue, will give their children an advantage. If they speak English perfectly, and if they only speak English, then that child may be advantaged in relationship to English, but the child will be disadvantaged in relationship to his mother tongue and the child will not benefit from the cognitive development that comes from speaking more than one language.
 Baker, Colin, Foundations of Bilingual Education and Bilingualism 4th Edition, (2007) Multilingual Matters Ltd., UTP 2250 Military Rd. Tonawanda, NY 14150