Your kid now is at a stage where he might be a victim to bullying. It is also the stage where your kid can themselves be a bully, hurting other kids. It can be devastating to any parent to hear being told their kid is a bully. But if you ever happen to hear about it should take actions rapidly and rationally.
What you need to know
As a parent watch out for the signs of bullying in your child. The first step in identifying if your kid is a bully is if they are found to be aggressive; understand the reason behind them behaving such way. Kids bully because of insecure reasons, because they want to have control over others which gives them a power of being mighty, and some do it because they do not understand that it is unacceptable behaviour.
What you need to do
Make them understand that bullying is not at all acceptable and they should not bully others. It arises due to the lack of self-control in themselves and with kids of angry nature. They do not have control over their feelings and will try to harm other kids also. Excessive exposure to crime, beatings etc on screen, TV, environment make kids develop this behaviour.
As at this age your kid is very curious and eager to learn many things, you need to monitor their activities. Check on the motives behind the behaviour or the influencing factor and curb that first. Talking to your kid helps a lot, remember that this is an early age and the child can be brought back to the right path if you take action immediately. Encourage good behaviour in them with praises. Teach them how to respect others feelings and show kindness.