Hmm.. I mean Children in the sense that they are not informed about all the facts. Is that not a requirement for a free market to work correctly ? Total Information Transparency ? Which requires them to understand the information..
The Children don't know if they eat all those sweets they will damage their bodies, get fat, rot teeth etc etc.. If they did - they'd think twice about it. And 'happily' choose to only eat a few.
They don't need "Total Information Transparency", they just need enough information to make a reasonable (not necessarily perfect) decision.
The market for fees doesn't exist yet, practically speaking. We have no tools to collect and distribute the necessary information. Mostly, this is because bitcoin is still young. It wasn't born fully formed; we still have work to do.
Allowing fees to float in relation to transaction value was a very wise decision. Setting a fixed percentage, even as just a floor, is impossible at best, and grotesquely disfiguring at worst.