Hi

My youngest is 4 but luckily she is very gentle with our kittens, probably because she has been brought up with rabbits and a dwarf hamster!

I would suggest that instead of punishing the 'rough' handling of them that you reward the 'gentle' handling either through charts that build up to a rewards or little rewards there and then whatever you think might work for her.

Also, have you taught her how to pick them up etc without hurting them?
My little one instinctively knows how to pick up and carry the kittens but i have had to show my friends children how to do it which has worked for them.

__________________