I have the same bug. It happens random no matter what the child does or if I zoom in or out.
I noticed the new 2 toned hairstyle worked great on my sim as a toddler but when I gave her the same hair as a child it doesn't stay on her head. It has a life of it's own and jumps around the house -- didn't want to have to change it because it's the only child hair that has that peach tone in it but it's rather disturbing.
I have all packs (except Weddings), a few kits, and all updates downloaded. Wasn't an issue until she aged up and sometimes it stays on her head but it spends a lot of time like 2/3 tiles away moving as if it was on her.
