No one likes to lose, but it is important for young children to learn how to accept loss without feeling bitter or bad about themselves. Begin by acknowledging your son's feelings and let him know that it is okay to feel disappointed, sad, or angry when he loses. Explain that while it is okay to have these feelings, it is not okay to get angry at the people he is playing with. Emphasize the importance of having fun and trying your best, and make sure your child understands that he cannot win all the time. A great way to encourage effort and fun over winning is by playing cooperative games -- non-competitive games where everyone works together rather than against each other (for e.g., “Snug as a Bug in a Rug” by Peaceable Kingdom and “About Face” by Eeboo).
