My DD (3yo) grabs her brother (1yo), pushes him over, a good few times a day. Sometimes she does it when I'm distracted (washing up say), sometimes when we're all playing beautifully. I know she's still dealing with having to share her mummy and her toys, but it's driving me up the wall. I try to pre-empt it but it can happen so quickly. I always say no, she gets time out or the toy is taken away (depending on the situation) and I give him lots of cuddles so all the attention is not on her. I try to be calm and tell her I don't like the behaviour, but it's wearing me down.
So is there anything else I can do?