This is scary.
1. easy child is learning that people you love might hit you.
2. It seems difficult child has at least some control and is choosing to hurt people.
3. He is targeting you when there are no adult witnesses.
Kanga got much worse as she got older. From 6-10, it was a random act only
once in a while. At 10, things started to escalate. Her first psychiatric hospital stay, she was 11. She was in Residential Treatment Center (RTC) by 13.5.
i would suggest implementing a safety plan. Lock up all knives, tools, etc. -- anything that can become a dealy weapon. Keep easy child under your direct, eyes on supervision at all times. Since husband has his head up his butt (as did mine back then), never leave both kids with him. Always take easy child with you, or hire someone to watch easy child at their house.
