One of the best birthdays my girls ever had (we usually do theirs together too, since they're nine days apart) was just hooking up the sprinklers and letting the kids run through them. I also bought a couple of flats of petunias and the kids potted them in cups. I made a sunflower cake out of a round and some twinkies, frosted yellow (Family Fun idea). I wish we could do that again! We didn't have grass in the backyard in time this year, though. Didn't think the parents would appreciate taking home muddy kids.