Twice Blessed: Language and Cognition

This doesn't seem to evidence that bilingualism is a critical factor in faster/earlier development of executive functions. Language just happens to be a very suitable vehicle for it -- because babies desperately try to synthesize the information around them, they have no choice but to attune to the sounds and try to make sense of them.

It is possible that language is the most suitable vehicle, but it remains a vehicle and not the principle component. You could possibly get the same outcome, if for every interaction with the baby, the father and the mother have habitually different behaviors. Dad always uses his left hand, mom always uses right. Dad always wears blue, mom always wears red. This is has similar executive control / perspective taking demands. Language is just a more flexible and ubiquitous version of this kind of categorical differentiation.

Or, turning this around, and I say this based on the behavior of many immigrant families I know, failure to maintain home bilingualism may be because of a weakness of executive functioning on the part of the parents. It takes a bit of discipline to set up cuing situations at home so that children learn to use both languages, when they know that one language suffices for communicating with the parents.