Helmets

At what point is a child a candidate for one of those full-time protective helmets?

The baby is learning to stand and balance and he isn't very good at it yet. Today he bumped his head on the tub, the window sill, the high chair, and he pulled the safety gate down on top of himself, among other more usual falls and knocks with his toys. I've spent all day comforting and kissing his boo-boos. This kid needs a helmet.