not to keep harping on this, but the 5th way would be do do an EM residency and stopping. i know that you won't be as strong in pediatrics but is tacking on a 2 year fellowship worth it? i guess for some.
finally, yes i know also of board certified em physicians who pick up a few shifts a month at a local dedicated children's er. mainly it's to try to keep up to date with their peds. truthfully, i don't find those em physicians working in a peds er vs adults er to be any more effective. i personally think a strong pediatric children's hospital ed should have primarily board certified ped er physicians. even if i could work all my shifts at a pediatric er, i wouldn't. as a matter of fact, i think most regular EM trained physicians wouldn't want to do solely peds.
i'm not sure where i'm going with this but basically i think if you love peds and hate adults but like er you should do pediatrics then possibly a peds er fellowship. if you like adults and er, do emergency medicine. see, per my point of view, you should just be done. why spend another 2 years to be board certified in EM and Ped EM? if you do an em residency, you will be able to see peds. and in most communities, pediatrics is a good 20-30% of er visits. in certain cities, philadelphia, for instance, there are three dedicated children's hospital er's that one sees very little peds in adult ed's, but that's not the case in the community.