It depends. If its your spouse, you talk with them. Maybe go to counseling with them. Disengage and let them do most of the stuff for their kid.

If it is bm, your dh can talk to her, but barring neglect/abuse, he can't do more than that.

Regardless of which parent it is, be kind to the kids. If you're religious, pray for them. If they show signs of wanting to get to know you, take them up on it.