Well that's simple. GO TO THE PARK! I'm watching my niece this weekend so we up from the normal three chitlens to four. Most of the time the kids play great together but just like an adult, they get sick of each other if they've done everything there is to do while stuck inside. Easiest way to cure this was to load all the kids up and take them out. It was six in the evening but I didn't care because it was gorgeous outside.