Knock 'Em Down Games
There are probably a thousand variations of this game, but they all have the same basic premise. Set up a booth, equip it with items to knock down and give contestants something to throw at the items. It sounds simple, and it is. Variations include posts or vertical objects you can throw rings at, holes you try to throw objects into and moving objects you try to hit. Prizes can be given out for reaching a certain score. Kids of different ages should have different lines behind which they have to stand, with little kids getting to stand closest.
Palm Reading
If there is an adult in your school or organization who has the gift of the ham, this is a great activity for kids. Put together a booth with blankets and trinkets all over it, and let the kids go inside to have their palms read by the mysterious stranger. If the person playing the palm reader is a teacher, she of course knows all of the kids and can tell them things about themselves. A transparent joke, but little kids never get tired of it and will appreciate the attention and the fun.
Dunk Tank
This idea requires the involvement of people who are good at construction, but it's a classic and always a crowd-pleaser. A dunk tank consists of a big tank of water with a seat over it supported by a lever connected to a target next to the tank. Contestants throw balls at the target and, if they hit the target hard enough, it trips the lever and the person on the seat gets dunked. Hilarity ensues. This theme is easily customized for situations or events. For example, when Citizens Against Bankers organize a dunk tank, they can obviously put a banker on the seat. The dunkee can also represent intangible objects such as a disease a group is fighting or an environmental problem.