Ever seen a two-year-old tattering around a garden? There might be a poison ivy, or rose bushes or hawthorne around the edges. There might be spades or secateurs lying on the lawn. The kid doesn't care. He just wants to play with all those brightly coloured things he sees. To him, the world is a safe place. And you might want to rush out and cut back all those sharp spiky plants so they can't hurt him, and you might want to clear away all those dangerous tools just in case, he picks them up and cut himself on them, but you know you shouldn't because if you keep doing that then he either will grow up thinking the can never hurt him, or he might go the other way, and think that everything is dangerous, and he should never go far from your side. So you just watch. And wait. And if he does get rush from the poison ivy or if he does cut his fingers off with the secateurs, then you get him to the hospital as quickly as you can, in the reasonably sure knowledge the he'll never make the same mistake again.