T.S.
5 kids is a PERFECT number for this age! Not too small at all.
How much do you want to spend? Not super unique, but... My five year old son LOVES the movies... we don't go to the theater that often, so he thinks its fabulous. I know he and his friends would be thrilled to all get to go to the movies together! You can get those little kid boxes so each kid gets there only little popcorn, soda and candy. Go for lunch before or icecream after, it'd be really special!