Researchers at Cornell University have concluded a study that examined the experiences children have with nature and their attitudes toward environmentalism as adults. They found that kids who participate in “wild” nature activities such as “camping, playing in the woods, hiking, walking, fishing and hunting” before age eleven are more likely to care about the environmental as adults. “Domesticated” activities such as gardening also have a positive impact, though not as great.
I’m not sure I’d take a child younger than eleven hunting, even if I supported it in the first place, but I’m all for the other activities. About.com has a good list of family camping resources, and the National Park Service has lots of kid-friendly educational resources to prepare your little rangers for their trips.