Great idea about limiting numbers, and a sausage sizzle is the easiest and cheapest!!!

If you can, arrange it all outside, even move the dining chairs outside, so except for toilet, no one needs to come in... i HATE poeple going in and out constantly...you will also have a place to take the boys for some quite time if need be!!

If you grab a big bucket thing of ice, fill it with soft drink cans etc, and arrange all the chairs around it and the food, they really shouldnt wander around too much either... even some old rugs and blankets in picnic fashion will encourage them to "congregate" in an area, rather than just random wandering.. if it can be made fun and casual, but easier for you, all the better my dear!!!