5 year old hitting his sister

I have a sweet well rounded boy.  He has never really gotten into trouble.  Latley he has been getting frustrated and today he hit his 2 year old sister.  I mean he punched her a few times.  I took away his favorite toys and we talked he said sorry to her...all of that but I am so worried.  Is this normal?  I am wondering if I was to hard on him?  What should I do?

[SL345]

You were not too hard on him. Teach him about other ways he can express his frustration and anger. Tell him that hitting hurts people's bodies and their feelings, too. Tell him the rule in your family is no hitting. And, then don't hit (my bias - we tell kids not to hit and then we hit them). Get a great children's book by a psychologist called Hands Are Not for Hitting by Martin Agassi. He'll improve as he matures if you keep working on it. Good luck and hang in there.