B.G.
Hi, A.,
With a larger group like that games and contests work well. Number off 2 or 3 teams and have a sack race (use pillowcases to hop in). Roll a ball across a room with hands behind your back. Most kids love activities that allow them to move. Even musical chairs can be a lot of fun. A costume contest is always a great idea.
Have a couple of "prizes" for the winners like Slime or candy eyeballs.
Be sure and ask several other adults to help with "crowd control", so you don't get overwhelmed.
Whatever you do, have fun with it. Good luck!
B. G. (mother of 8, grandmother of 4)