Both parents play an important role in their child's language development. If the mother spends more time with the children than the father, the language she speaks to the children will probably have more of an impact than the language the father speaks to the children. However, this does not mean that the father's language will not or cannot be acquired by the children. One researcher's personal experiences raising his own children to speak his non-native German while living in Australia offers evidence that the father does make a significant contribution in the language development of his children. But perhaps the most compelling evidence in Saunders' book of the fact that a father can teach his language to his children is the reported results of his study of his own children, who surprisingly learned to speak well in German, even though practically their only exposure to the language can from their father, and not from the mother, who spent four to six times more time with the children, and not from the Australian community where they were reared.
Children have the capacity to develop new language more naturally than do adults.
Additionally, they acquire a piece of a second language, generally learning far more of that language far more quickly than an adult could. How well a bilingual child develops their second language can vary from a child who only knows a few phrases and some very basic vocabulary in a second language, to a child who listens and understands, but cannot or perhaps will not speak, to a balanced bilingual child who communicates in both languages with the same command as monolingual peers in both languages. Whether a bilingual child is just dipping their toe into a second language, or actually swimming in it, that child is experiencing to some degree the richness of another language. Children that are exposed to more than one language, even if they never fully learn that language as children, have a higher capacity for foreign language learning as teens or adults. Just playing foreign language cassettes in the home, and trying to speak whatever you know of a second language to your infants and young children will help their minds expand linguistically in a way that will give them an educational advantage later.