Pediatrics for EM providers is generally underrepresented in their training. Most of the data I've seen has shown that Pediatric patients account for ~25-30% of all patients seen (talking community ED's here) but pediatric exposure in residency is about 10% of training time. I'll add that it is a near universal complaint from EM residents that they dislike the diminished autonomy they get while on their pediatric rotations (Peds ED shifts, Peds wards, and PICU), which probably through a combination of too much oversight and lack of buy-in from the EM residents further limits the overall educational value of that time at the children's hospital. I certainly saw that in my time as a peds resident and PICU fellow.
That's not to say that a peds residency->peds EM fellowship is super warranted either, as another recent study has shown that practicing, fellowship trained, Peds EM providers rarely use their advanced training in terms of numbers of intubations, chest tubes, trauma management, and so on. Mileage may vary for those Peds EM providers in community hospitals without robust peds subspecialty coverage such as peds surgery and in-house PICU staff. As of now, it's entirely unclear what that should mean for Peds EM fellowships, but there is at least a handful of people out there suggesting that the training for Peds EM should change dramatically. I think that for now, the job market for Peds EM trained people, regardless of which direction you go, is actually probably pretty stable as the aforementioned number of peds ED visits isn't likely to change, and hospitals can advertise that they have pediatric trained EM specialists available, which parents eat up.
If trying to decide between the two, the biggest ? to answer is, do you want to see adults as a major portion of your training? If you're meant to be a pediatrician, then you'll say no, and you'll have your answer.
