When I was growing up, a family in my town suffered through the death of two out of four of their children. The first loss was due to their four year old unbuckling their infant without them knowing and then asking to roll down the window. She, the four year old, chucked the baby out of the window while on a country road doing 55. Three years later, they had another baby and the daughter, now seven, drowned the baby in a toilet while the mother was cooking dinner.
I don't know what I'd do as a parent in that situation, but if my child killed half my kids and didn't seem to ever show signs of remorse, I'd try and get her help, but I don't think I could honestly look at her without constantly being reminded of everything that had happened.
This is probably a different situation.