Twenty plus years ago when my childhood best friend had her first baby, her family decided to raise him to be bilingual. Her parents are from the island of Mauritius so her father only spoke to him in French while everyone else spoke to him in English.
I witnessed for myself the little boy as a toddler looking up to the light bulb twice – when we asked him where it was in English and then when his grandfather asked him in French. It’s fascinating to me how children can pick up things so easily. Apparently Ashton Kutcher’s little girl is especially bright but his son, hmm, maybe not so much.