I was aghast after learning Korean and proper ways to speak to elders when my native Korean spouse spoke to her mother in 반말. But it doesn't seem that the majority of children speak formally to their parents.
I want my children to learn the right way, and they struggle with 존댓말 since they primarily only use 반말 at home.
From experience raising children to speak Korean, please give findings on forcing 존댓말 (or not forcing 존댓말) and the results thereof as it pertains to teaching children to speak Korean.