we have had both DD's parties outside - we have tarps we can put up to close off the undercover area if it's crummy weather, will clean up the shed if really necessary - and we put massive picnic rugs under her slide last year so the kids didn't get wet tushies! it was cool, but not cold, the rain held off for the day - and the kids loved being outside. we just suggested to people to have a change of clothes in case kids fell over in mud (most do this anyway!). we have room inside to a degree (we can move furniture to make it kind of an open area) but kids don't like being stuck inside so if i can kick them out, why not?

clean up outside is soooooo much easier too!