At this stage, your kid's social skills along with mental and physical skills are developing. Your child now enjoys making friends and being a friend.
What you need to know:
Your kid now enjoys sharing his toys and takes turns while playing. Pretend play and other forms are a part of his play time. While playing your kid may lose and he may start to yell phrases like 'Not fair', ‘You cheated’ or ‘ I will not play with you’. He may cheat or bend rules. There could be fights, pushing and also name calling. He could become aggressive. Most of the times these problems get solved on their own without adult intervention. If things don’t calm down then it would be a good idea to intervene and settle the problem in a positive way.
If you find your kid not able to lose graciously. Help him calm down and also give him lots of practice in this area. Play games with him and make him understand that how playing is more fun than winning or losing. Since the concept of losing is new to your kid, it may take sometime for him to overcome it. As time goes it will become easier for him.