Are you referring to handling any EM case, adults included? Or any peds EM case?
A good portion of the kids that come to the ED are things that could be handled by a general pediatrician in their clinic (ear infections, rashes, gastroenteritis, viral infections, mild asthma exacerbations), but the benefit of being in the ED is that you don't have to send the kid out for labs or imaging, and you may have consult services that can come down to the ED. Of course there are the real medical emergencies that should be in the ED and not the clinic, which a general pediatrician should still be able to handle. I think the major learning curve would be the traumas, as general pediatricians typically don't get ATLS trained, but if you're moonlighting in a community hospital, you're not going to be seeing the traumas that a Level I-II trauma center would be seeing. All the serious traumas come to our ED, not to the community hospital ED down the way.