A: At the age of 4, your child is still struggling with how to handle aggression. Aggression is normal. But it's up to us as parents to show our kids how to channel that aggression. Give him the opportunity to get his aggression out in acceptable ways -- running, pounding clay, singing and shouting outside -- and set limits about what is acceptable behavior.
Don't expect him to "understand" and "tell the truth" at this age -- if he fibs about his intentions, don't confront him. Instead, say, "I know you wish you didn't hurt him, but you did, and in our family when you hurt a child you need to take a time-out." Then, stay close at hand to monitor him and intervene when necessary. You're acting as his "supplemental stop signal" -- helping him to stop his behavior before he gets out of hand. Over time, he will internalize your limits and start to set his own limits better.