Here you go, good news about raising multilingual kids: “A study just published in the Proceedings of the National Academy of Sciences says that some aspects of the cognitive development of infants raised in a bilingual household must be undergoing acceleration in order to manage which of the two languages they are dealing with. The aspect of cognition in question is part of what is termed the brain’s “executive function”. This allows people to organise, plan, prioritise activity, shift their attention from one thing to another and suppress habitual responses.”
The study was done with 7-month old babies.