Al-‘Allaamah Ibn ‘Uthaymin (رحمه الله تعالى) said:

“The Messenger of Allah (ﷺ) said:

“O young boy, say Bismillah, and eat with your right hand.”

Know that when manners and etiquettes are taught to a child at a young age, they are not easily forgotten. A child will not forget what you teach him while he is young. However, when he grows older, it is possible that he may forget what you taught him, or even show some resistance. But whilst he is still young, he is more likely to be responsive and accepting of what you teach him.”

Sharh Riyadh as-Salihin, vol. 3, p. 172