They usually feel good about themselves and start to develop the concept of give and take. Organize a play group in your home with mutual friends or consider a preschool setting. Get the child and bring him into the group, staying there awhile. Invite a friend over to play. If going over to someone else's house is threatening to a young preschooler, go along to bridge the insecurity gap.
Young children can be very possessive and unwilling to share toys.
Have a talk before a playmate arrives. Ask what special toys the child would rather not share. Put those away. Explain that the remainer will need to be shared. In The Elementary School Years Elementary children often vie for control and may find it hard to agree on what to play.