Most 13 y.o.kids I know are a bit to old or big for a bounce house, but maybe your son and his peers still enjoy it. I have done pinatas with multiple classrooms full of kids with no problems but to control the chaos and increase safety I give instructions that no one may move after the pinata breaks until I blow a whistle (and the stick has been removed from the hitter!. If a wide range of ages is participating I give each kid a bag to gather treats in and that is all they may grab. This keeps the big kids from grabbing everything and the little ones from getting nothing. It's a good idea to keep some candy on the side to supplement the kids who get very little.
You should have some type of basketball shooting contest. Buy one of those portable baskets at Toys R Us and have a 3 point contest or something.
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