We mix up both, but speak mainly French at home. Ds goes to English kindy 2.5 hours a day, though. Ds has an accent in both languages
so this may not have been the best route accent wise (as I have an accent in French, and dh has an accent in English). However, vocabulary wise ds is definitely balanced 50:50. There is no word he knows in only one language. He even knows that Smurfs are Schtroumpfs
Whenever a new word comes up (in an obvious way, sometimes you don't notice but if he asks, what's that?) we tell him the word in both English and French.
EVERYONE said ds wouldn't speak till he was 3, but he was adressing all family members (parents, grandparents, greatgrandparents and cousins, uncles, aunts...) in their preferred language, in full sentences, at 26 months (I keep obsessive language notes, took psycho linguistics when he was little).
He's also beginning to read (e.g. Dr. Seuss type books) and write (phonetically) in both languages. I used to worry. Now I just wish he'd stop talking sometimes.
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