I think your question is on how to develop empathy in children.
Parents are key in a child development. They are who the child sees every day and try to imitate. The child tries to copy what the parents do. This with teaching the child what empathy is all about helps develop the child well.
Let the child know what empathy is all about. Relate it with what the child can see. Pictures get stucked in the memory than any other thing.
When the child is moody or going through some pains the parent should show empathy. The child will learn from that and learn to be sympathetic with others.
Incentivising the child for empathetic behaviour. The child will be eager to do the same again. Children loves gift and will continue doing the same actions that gave them the first gift.