Your child seems to understand that the language of instruction in the country where you live and at the school he attends is a more prestigious language. This situation is seen in almost every society that receives immigration.
But our advice to you is this: Even if your child answers your questions in the language of the country you are in, always speak Turkish with him and emphasize that Turkish is a family heritage.
Send your child to Turkish lessons/courses given in your neighborhood or school, and try to support what is done at school at home.
Prof. Dr. Belma Haznedar