If you have more than 1 trampoline you can play 'drop', with a small bean bag or soft ball. Everyone bounces and whoever has the ball throws it to someone else, who has to catch (neither may stop bouncing to throw or catch). If they miss then the thrower amd catcher get down, next person gets up. This keeps everyone engaged as catching while jumping is HARD. As EU improve you can add stuff to make it harder - full twist and then throw, only one bounce before you throw, etc.
You can also do races where they bounce along the lines of the metre box (can have 2 on one tramp if you're comfortable with that - I'm generally not so I have them race on 2 adjacent trampolines) in a seat landing position, pushing along to bounce on their bottom using their hands. This can be made more difficult by having them turn - I generally have them go along the tramp 3 times - first and second time they touch the mat with their hand when they turn, to finish its the first person to touch with any body part, and since I have them go feet first, it's generally their feet.
You can have them do challenges (which are also great for conditioning!) how many tuck jumps can you do in 30 seconds? <- great Ab and quad conditioning if they do them really low, how many seat landings, seat ->fronts, back bounces etc.