Less-lawn solution: For many kids today, what's missing from their lives isn't a play structure or a sports field (parks and after-school activities offer plenty of that), but the chance for a one-on-one connection with nature.
In that sense, a small flower or vegetable garden or, for older kids, a backyard pond that supports fish, frogs, or other wetland creatures can provide more lasting play value than a lawn alone. A low, freestanding deck connected to the rest of the yard with paths that wind among shrubs can serve as a base for forts or a stage for plays.
For toddlers, an oversize sandbox is a great choice. Cover it with bird netting, rather than plastic sheeting, between uses to keep cats and other critters from using it as a litter box while permitting sunlight, a natural sanitizer, to reach the sand.