My four year- old son is really aggressive when I take him on play dates. He pushes other kids down and takes toys from them without asking. Any suggestions?

Consistency is the key to good behavior.  Every time you observe these aggressive actions stop what you’re doing and pull him out of the situation for a brief time out (five minutes away from his peers) while explaining what he did wrong.  Before allowing him to play again have him tell you why he was in time out so that he becomes aware that he is accountable for his actions.  Repeat as often as needed.  It’s important for both parents and care givers to be completely consistent until the behaviors disappear.