In an article from The Economist, Lane Green discusses the strategies, challenges, and rewards that he and his Danish-speaking wife observe while raising their two children in a bilingual home. His son makes some cute errors, applying the grammar of Danish to English vocabulary, resulting in phrases like "Come heredown."
This interaction between two languages is called language transfer and many English learners do the same. Spanish and Portuguese speakers will often say to their teacher, "I have a doubt," when the more natural English phrase would be "I have a question." Chinese speakers will often use back as a verb, as they can in Chinese, creating sentences like "I back my home."
In the Economist article, Green mentions misguided teachers and doctors who warn parents to only speak the majority language with their children. This is based on the false idea that bilingualism can somehow harm children. The fact that children are learning two vocabularies simultaneously means that they might make errors (like "heredown") that their monolingual peers do not. But this is a temporary delay.
The research in fact supports the Greens' intuition, that bilingualism has many cognitive benefits. These include "enhanced attention control," “enhanced perceptual attentiveness,” and better spatial reasoning, among many others.
In the second half of the article, Green discusses some fascinating research on the development of bilingual children's minds. Read the whole article at the Economist!