Scott Anderson of Desiring God Ministries interviews Elyse Fitzpatrick on her new book, Give Them Grace, and asks her those kinds of questions. You might be surprised, or even appalled, at her answers. Whether or not you agree with her conclusions, I think you'll see that they emerge from a biblical understanding of human depravity and the Spirit's work in accomplishing regeneration. I hope you'll find it thought-provoking and maybe let it simmer for a bit.
The bottom line: Fitzpatrick is convinced that we focus far too much on behavior and teach far too little on the gospel as we go about our parenting labors. Her point isn't that we shouldn't train behavior, but that we must lead our kids to understand that, apart from God's work in them, they really can't change in any meaningful way. And even if they could, it wouldn't get them anywhere with God.
Speaking from some experience as one of the formerly people-pleasing and falsely-professing-Christ kids Fitzpatrick describes (the "older brothers" and outwardly religious Pharisees), I think she's on to something. Video is embedded below, but this DG post has some helpful time-stamps.