Make the most of walks. Park a few blocks away from school or a birthday party. On the way in, ask your child what he sees, hears, and smells, or challenge him to a game of "I Spy" ("I spy two things that are puffy and white!").
Plant a mini-garden. Even a small pot on a back porch or windowsill can do the trick. Peas and catnip are notoriously good sprouters.
Invest in a few tools. For under 20 bucks, you can buy a toy-store bug viewer. Or try a pair of binoculars turned around, which magnify.
Visit the water's edge. Find the nearest beach, pond, lake, or puddle and plant yourselves beside it -- you'll be surprised how a pool of water sparks kids' curiosity.
Find nature near you. At GreenHour.com, a new site from the National Wildlife Federation, you'll find easy suggestions -- many from other parents -- for activities kids can do right outside your door, no matter what the season, whether you live in a suburb or a city. Click on "NatureFind" to locate a park or recreational area near you.