Your child is now at the stage where he understands emotions as well as empathy, and thus, can understand and indulge into acts of kindness, which is a wonderful human quality. Being kind is a basic aspect of humanity. It is our duty to teach our kids to be kind and humane. We should teach them to become more compassionate and considerate about others.
What you need to do
Guide your child not to make fun of others, but rather to help them out in difficult situations. If someone falls down while walking, then it is unkind to laugh at them, instead help them to get up and walk. Always teach them to be helpful with their siblings and friends.
For this you can also arrange practical tasks for the kids. For example, you can arrange a treasure hunt where the kids need to cooperate with each other to complete it. Such tasks will teach them to be interdependent on each other. Whenever possible you should act kindly towards others. This will set a live example for your young kids.