Vacation to New York?

I am 20 years old and have gone to New York City many times, one of my favorite places. Now, I am bringing my dad (who has been there many times as well), 7 year old brother, and friend. My brother and friend have never been, and I want to do as much as I can with them in the 4 days we are there. It is also my friends birthday, so we want to do something fun. Any good broadway shows for the whole family? What is something fun we can do for my friends birthday? And, is there anything we need to do? Any ideas for a great time are appreciated. :)