Hi Charles,
Do you know the Genki English site? It has some great games for kids of around this age. to practice various grammatical structures and so on. Check it out.
I agree with cheezels, you definitely need a break half way through of 5-10 minutes to give the kids a chance to go to the loo, have a drink of water, stretch their legs and run around outside so they can burn off some of that excess energy.
I would also include a story time, my kids love simple story books that they can understand. How about getting them to act out the story afterwards, either themselves, using puppets, or on a feltboard (the latter takes quite a bit of preparation as you have to make all the relevant pieces).
Do you have picture flashcards for the language you want/have to teach? I know lots of fun games that are FC specific so if you want more ideas for those just send me a PM.
Do you have a strict syllabus to follow or can you incorporate some more refreshing activities to give the students a change of pace during that long 3 hours? For example you could teach them how to make an origami something in English, take them outside for them to find things and say in Eng. (I have a couple of prints to be used in this way), watch a Mr. Bean video and do a follow up that is suitable to their level and so on.
All from me at the moment but if I think of anything else I �ll let you know.
Good luck!