A: Young children are naturally aggressive, but this doesn't mean we should allow it. This is the opportunity to show him, by your actions, how he can channel his aggression into socially acceptable behavior. It's also an opportunity for you to be more involved in his social interactions until he's more able to handle them himself.
At ages 2 and 3, it's important to show children how to resolve conflicts. Think of yourself as a mediator and teacher who is demonstrating how to resolve a problem. As soon as the kids get together, set the rules for how the playdate will go and be present to help settle any problems. Have the kids act out a good way to handle disagreements. Look them in the eye, be positive, praise them for a good effort, and don't scold. If they can't follow the rules, separate them in a matter-of-fact way. Yelling and drama only increases the chances the aggression will happen more. You can also enlist other older kids to help show your son how big kids get along. They are the best role models you can get!