RL agents are exposed to millions upon millions of stimuli, almost all of which will be 'painful' at least initially (according to the websites definition of pain). I think for children negative stimuli are not all painful, pain is a certain small subset of negative stimuli that damage is being done.
I think children are constantly experiencing rewards and punishments of a sort analagous to reinforcement learning. Until a certain age their brain is hardwired to want to please their parents, so they pay a lot of attention to the parents' faces, and find reward in smiles and find punishment in frowns. After that, they are driven by a certain amount of ego, and find reward in self-accomplishment and find punishment in being told what to do.
