I'll write down the two ideas I came up with before I head to bed:
1. A good game for some of our younger characters could be a sort of bobbing for apples, only wizard-style. Instead of being inside a tub of water, the apples could be bewitched to hover in the air and the children have to jump for them. The rules of using only your mouth would still apply. As a reward for capturing an apple, each apple could have an enchantment that will transform the child into a super-cool outfit for a few hours...or the apples could do something else. I just thought it'd be cool if the apples rewarded the child in some way when it was caught.
2. A Halloween Quidditch game. Unlike regular Quidditch, there would be no quaffle. Instead, the chasers would play with a bewitched pumpkin, and if the pumpkin stays in the same chaser's hands for too long, it will explode and that chaser will be kicked out of the game. Kind of like hot-potato on broomsticks. Still have a keeper and bludgers and the snitch, but the exploding pumpkin would just kind of add an extra fun element to the game.