My elder one is always bullying his sister, how can I improve the situation?

Hi, may I ask what your kids ages are? If you elder child is older than 5 years old, his understanding level will be enough to know that his actions are wrong. It is best to make your child feel empathic by explaining why he shouldn't bully his sister.Tell him that if he hits his sister it'll hurt her. He might be struggling to communicate with his sibling and when she doesn't talk or communicate back with him, he must be feeling frustrated. It is however best to always keep an eye on the two kids.