Start introducing the concept of sharing, by sharing a snack with your child and using the word “share” to describe the action. If your child is actively fighting with another child over a particular toy, remove the toy altogether and shift their attention onto something else. Do not assign blame to anyone, rather imply that the toy “needs a rest”. Try to avoid possible ownership conflicts over toys, by removing your child's favourite toys from play. There is less chance of fighting over toys that are not considered important to either of the children.
Always point out adults or older children who are sharing things, to your child. If your child has a friend visiting, arrange for activities that don't involve formal sharing, such as playing with dough, or drawing. If your child does share, even if it’s not intentional, be sure to give praise and encouragement. This teaches your child that sharing is good and that is makes people, especially you, happy.