With so many little ones, you have to keep the activities coming one right after the other. At 4 yrs old, you are going to have to make it Gymboree like. All activities will need mommy's help. You can sit them down and play hot potato with music. Pass the potato or ball from one child to the next. The one left holding the potato when the music stops is out. The remaining child will be the winner and get a prize. If you are bringing chairs to the site, you can do the same with musical chairs. You can have a prize hunt. Get little prizes at Party City or online at oriental trading, wrap them up and hide them in a particular area of the party area. You can have relay races. Have the kids hold an egg in their hands instead of on a spoon, or the spoon if you think they can handle it and make 2 or 3 teams and they have to walk or run back and forth passing the egg and the winning team gets a prize. You can get great stuff for mini prizes at orientaltrading.com. If not, you can get a 24 piece puzzle or a board game like candyland or hi ho cherrio to give as main prizes. You could also have a dance off. Play music and tell them to give you their hottest hip hop moves or break dance routines and have 2 grown ups judge the contest. This one usually gets them tired out and you can prolong it as long as you like. You can also face paint. Good luck and have a ball!!