In our unit we usually premedicate with atropine, sedate with either fentanyl, ketamine or thiopental (depends on the physician preference) and paralyse with succinylcholine or rocuronium (depends on why the kid crashed, what else we know about the kid, physician preference).
For us? Usually fentanyl and versed for sedation with vec for paralysis. Occasionaly succs, but not the first choice. Little ones we premed with atropine too, but that's a physician choice. Occasionally we'll use etomidate for sedation. We're kind of a mixed bag.
ETA: We almost never sedate with just one thing. Generally it's an opioid and a benzo together. Only exceptions are kids with no blood pressure.
Our RSIs usually begin with atropine, then versed. We used to use vec almost exclusively. We have acquired 3 new intensivists who prefer roc. We don't use succ. On a rare occasion we've used etomidate.
We have pre-printed code/RSI drug sheets based on pt weight in each room with the dose in mg and the volume amt of each drug. These are Excel format and were developed by one of our intensivists and our Peds PharmD, making administration in a crisis simpler.
Our unit typically uses fentanyl, versed, and rocuronium. Atropine prior to intubation is used for the neos and infants. As others have said, it is physician pref, as etomidate and vecuronium is also used, but not as frequent as the three listed above. Roc has a much quicker onset of action and a shorter half-life than vec, so that's why our intensivist choose roc.
We do the same combo (fent, versed, vec or roc). However we usually don't premed with atropine, even in infants. We just have it drawn up at bedside per physician preference. Also we have a RSI med kit/box that contains all the meds listed plus epi and more.