bruised bottoms?

[Nmd]

At the risk of sounding a bit dim, why don't babies at the toddle-toddle-crash stage of walking have permanently bruised bottoms? I find it difficult to believe that a little layer of nappy is enough to protect two stone of baby landing hard!

Maybe because they have more padding there naturally as well? Our son was covered in bruises when at this stage (he is now usually so interested in what he is holding that he walks into doorframes etc instead) but not on his bot.
And there was that case of a toddler who fell out of an upstairs window onto concrete and escaped with a few bumps because she landed on a full overnight nappy. A rationale for not changing them til they are sopping if ever I found one.