A great outdoor alternative would be to buy minimalist baby footwear (does that even exist?) or even let them mosey around in thick socks. Vibram Five Fingers will be coming out with kids line, which you can check out here. Vivo Barefoot also has a kids line that you can see here.
One advantage of letting babies and toddler go barefoot is that they receive feedback from the soles of their feet, allowing them to keep their heads up, which prevents falling down. Who wouldn't want their baby to learn to walk earlier? Also, most shoes are too tight on kids, thus deforming their feet. It's not as bad as foot binding, but sneakers don't allow the toes to spread out and let the foot muscles fully develop.
What do you think?