Slip-N-Slide. Use a $10 10x25ft tarp for your slip-n-slide. Use something heavy to hold down the corners, but stakes are best. Use liquid dish soap from the Dollar Store to help the kids slide faster and farther.
Piñata. Assemble baggies of treats so that all the kids get the same amount. This should cut down on the “I didn’t get as much as him” comments.