Just that really, my son (four next month) has always hurt his baby sister, when she was born 15 months ago I expected it a little bit and the first year was really tough if they were together even if I was in the room he would push her, pinch her, hit her etc which obviously I told him off for. Now I would say that it's not quite so bad and sometimes he can be affectionate with her or tickle her but often he will push her out of the way, try to squash her and do things like bend her hand backwards when we are in the car (he will lean over in his car seat). He seems to do it more when he is bored. I know people may say he is doing it for a reaction but I can't not react when he is doing that, and will put him on the naughty step and explain why it is wrong and make him say sorry to her afterwards, which he will.
Anyway does this sound normal? I was thinking when she was first born that it wouldn't be unusual, and he was 2 1/2 then, but he is still doing it.
And any tips on how to stop him?