Serious attitude
You might think it is funny, perhaps cute, to watch your immature three-year-old push his taller, larger, more capable sister off her chair so that he can sit there himself, but it is not funny.
When he sees you smile at (or even ignore) this sort of behaviour, he thinks you approve and continues with it.
Zero tolerance
Clamp down hard on instances of bullying among your children. In particular, do not allow any form of physical violence between them.
Your younger child should clearly understand that hitting his sister is always unacceptable (and vice versa, of course).
Cooperation
Stimulate co-operation, not competition. Encourage your children to play a board game together, or to watch a video together.
Praise your younger child when he is positive towards his older sibling on these occasions
Explain
Tell your younger child why he should not hit, tease or deliberately upset his big sister. Explain that it makes her feel sad, and that she loves him and wants him to love her, too.
Point out that he would be unhappy if someone did those sorts of things to him.
This article was first published in Young Parents.