A castle bounce floor with a slide off the side and a large pool at the bottom, so the three-year-old who will not go near the slide still has somewhere to be. That is the case for a combo generally: mixed-age birthdays are the common kind, and one unit covering both ends of a guest list beats two units crammed into the same yard. Runs wet or dry, needs 37 × 21 ft of level ground and a single outlet. Ages 3 and up.