The thing is, the way perps are made to confess is by LE softening the possible circumstances of the crime: "Hey, man, everyone has a point where a kid just gets on their nerves. No one in this room is going to hate you for that. We've all been there. The kid seems like she/he could have been a real handful. If you snapped, it happens. We'll understand. But now is the time to let us know so we can bring closure to this case. Did something like that happen? Did you get to your breaking point?"
They often get perps to confess this way and the perps often soften their confession as a result. They minimize what they have done so they can retain some sort of rapport with the good ol' boys who have been questioning them for so many hours. They know they are caught but think if they minimize what they did and why, they won't seem so evil. It's a psychology thing and it appears to work. The cops give them a way out of the truth but a way that still allows them to locate the child they are desperately seeking and put the perp in prison.
I agree. I did read somewhere, but it may have been FB, that the step sister is with other family now. I guess her paternal family. Hopefully they are taking care of whatever needs to be done.