My uni has a 2-week kids camp every summer and winter, and I've managed to avoid it for the past couple years, but this year: it was time. I have a homeroom class for 4.5 hours/day and a special Content-Based Learning Class for 1.5 hours/day, which is with different groups each day.
For that special session, I chose "Arts + Crafts" and have been making paper masks, complete with sparkles, glitter and straws and anything else fun that I could find in the teacher's room. I highly recommend it, as it is quite easy to organize, requires minimal "teacher-talk-time," and it keeps the kids entertained for at least an hour.
For the homeroom morning session (3 hours), there are no books, materials or anything else prepared by the camp, but it's entirely up to me. I do some study time, with a variety of speaking/listening/reading/writing activities. I try to do one worksheet or puzzle and then a game of some sort. I try to alternate the games between whole class ones and ones that they can play with a partner or small group. I chose a few themes such as animals, numbers from 0-1000, body parts, and months/days of the week/seasons And then I have about 30 minutes of "free-time" before lunch. I have a variety of card and board games that they can choose from.
In the 1.5 hour afternoon session, I read an Internet story with them (I like www.bedtime-story.com), which takes about 20 minutes or so. I go around the class and have them each read a couple of lines until the story is finished. Then, we have a bit of practice time for the final performance. And to finish it off, about 30 minutes of movie time.
The best tip I can give for a camp like this is to have a "stack." I had my TA do a massive amount of photocopying for me on the second day of camp and now in the morning, I just pick a few things that I want to do that day. It makes life much easier, instead of scrambling around trying to figure stuff out 20 minutes before class and having a line-up at the photocopier.