There is a rabbinic obligation on the father to educate his child to fulfill mitzvot even before he is Bar Mitzvah'ed or she is Bat Mitzvah'ed. The age at which this obligation begins varies according to the mitzvah. Below are the details of this mitzvah.
- Some say that children from the age of 6 should say Birkat Hamazon. 
- Rabbi Mansour on dailyhalacha.com writes that parents should ensure that children from the age of 6 say Birkat HaMazon.