I have no idea what goes on with the childrens, but here's what our PA/NP's do in the MICU/CVICU and Neuro ICU:
*First, I must mention that my hospital (UCSF, no sense hiding it I suppose) has an "open ICU". It's an odd set up and I (plus almost everyone else) hates it, but essentially it means that any following team can write orders for a patient in the ICU. So typically the primary team continues to follow up to ICU, along with any consulting teams, while the actual "ICU team" (which is run by Anesthesia but the residents are typically a mix of Anesthesia/Medicine/Emergency Medicine) is responsible for Airway, Blood Pressure, CRRT, sedation, tube/line insertion, other random things, and "ICU medications" that don't fall strictly under Cardiothoracic or Neurosurgery.) Confused? So are we. Anyway, moving forward...
On our Med-Surg unit the NP/PA is interchangeable with the ICU Resident. Airway wise they write the ventilator orders, they can intubate if needed, order to extubate, and order different respiratory therapies and medications. They manage all the vasoactive drips. If Renal lets them they can also manage the CRRT. They can run a code blue. They insert central venous/trialysis catheters and arterial lines. In essence, they make sure the patient is still breathing and hemodynamically stable through the night (or day). Since they also follow every ICU patient, I've noticed they tend to do a lot of "shepherding" of the other teams as well, making sure every team is on the same page and all the proper teams/ancillary teams are consulted. On the cardiac ICU, there is a specific PA that is solely responsible for the ECMO's.
On occasion a patient will be "Primary ICU" - in which case ICU manages everything - which means the PA/NP is literally managing everything, but those patients are exceedingly rare and I've only ever seen it happen a couple times. Both were homeless direct from the ED to ICU admits with a Ddx of "He's sick everywhere, and uh, we don't know why?" (I'm 99% convinced it's just because no other team wanted them...)
But I have to ask, if you like skin disorders why not just go into derm? Or if you're queasy, why not something like primary care?