Zoebird - good point about four season play! My kids play in all weather, too - they just dress properly for it. They go out at 10 at night on weekends in the winter and build snow tunnels for 2 hours, and play in the summer rain (no thunderstorms, folks - just rain), stomp puddles in wellies in the fall and spring, and everything in between. The only kind of weather I don't allow them to go out in is obviously dangerous weather like tornado warnings, hail, lightning storms, and the like that afflicts Ohio.
Also - "dirt" is not a four letter word in my household. I actually encourage getting dirty. I got rid of the previous owners' precious wall-to-wall carpeting and chose easy-to-clean floors for this country house. I have personally seen parents who actively discourage hard play in favor of keeping designer kid duds and their interior decorating pristine. As for me - the health of my kids comes before showing off.
I have a mantra that I have spouted for years... "If I eat right, I feel right. If I feel right, I exercise right. If I exercise right, I think right. If I think right, I eat right..." Phil-SC