Gosh, I don't know that I could give a figure. Ummm a lot.
DS has a superb imagination and loves to play outside with his trucks or rides his bikes. Often the big and the little girl are out there with him. I have big back windows and a kids safe yard that is fully fenced. Weather here isn't an issue unless it's a million degrees but even then they seem to stick to covered areas.

I generally loosely direct (find supplies/games/toys, instruct, help if they need or ask) if they are after something to do. I don't play with them often. They set up something and play near where I am occasionally but they're all pretty independent here. I play most with them outside.