Your child's temperament will start to show at this age. Each child is unique and you shouldn't expect your child to behave in a manner that is contrary to their nature. Support your child's way dealing with the world, instead of pressurising them to behave differently. By being sympathetic and understanding, your child will feel more confident and secure.
Children will want to socialise more as they get older. Your child will start identifying playmates as real friends and start treating them with kindness or affection. Sharing is an action that starts to take tangible meaning with friends and this helps with social development.
Your child might go through the stage of having imaginary friends. This is fairly common among children without siblings. It is normal behaviour and generally disappears by the age of six. The imaginary friend is used by your child as a platform for dealing with personal issues and helps your child build a value system and a conscience. Your child's imaginary friend can be a companion in times of loneliness or sadness, or can become the scapegoat for unwanted actions or behaviour.