Your child is going through a very exciting period of life. At this age, he's becoming aware of the fact that they are separate individuals from their parents. As your child starts to understand this concept the need for self-assertion will become dominant. Your child will increasingly communicate likes and dislikes. There would be a continuous effort to act independently. However this is also the time when children have just started learning important skills like sharing, communicating, waiting, etc. These skills are still in their nascent stage and need a lot more work. As a result children this age feel a lot of frustration.
What you need to know
There would be some embarrassing incidents that you would face as parents when your child hits another child in the playground. Hitting is a common phenomenon for many children this age as aggression is a normal part of child development. With their primitive language skills and a strong desire to be independent, many children this age feel frustrated and impulsively hit out. This seems to them as only way to communicate their feelings.
What you need to do
While hitting others is not okay and should not be allowed, do not be judgemental just because your child hit some other child. This does not mean that your child is a bully. It just means that your child still needs to learn some more life skills. By consistently letting your child know that aggressive behaviour is not allowed and suggesting different ways to express emotions, you will help your child learn to deal with emotions.