Funny, because I almost see this as an argument NOT to go into PICU, since that's where the CP/MR/trach/G-tube & fundo/non-interactive spastic quadriplegics seem to like to hang out. But hey, to each their own. With the legitimately interesting kids, I can definitely see the appeal.
I have to reiterate what others have said, though: kids are kids, and the way we work with them is just different from the way things work anywhere else. I know my medicine, but I have trouble being stern and straight-laced; anywhere else, that would be a failing to an extent, but in Peds it's an asset. This is where medicine and personality meet, and while it always matters that you give the right treatment for a problem, often the way you give it matters almost as much to the family or the patient.
The highs are the unexpectedly good outcomes or reactions that it seems only kids are capable of. Going from the brink of death to bouncing around the playroom in a matter of a day or two. Lying around after some crazy procedure, still showing their personality when an adult would be immobile and begging for more Dilaudid. Stoically going through a chemotherapy regimen they couldn't begin to comprehend, making the most gut-wrenchingly benign requests ("Can you play a game of Sorry with me tonight?" from a girl who recently got a bone marrow transplant).
The lows are twofold: one, when things go wrong or just turn out badly, it hurts. That goes almost without saying. The other part is that there are some aspects of Peds where you don't always really feel like a doctor at all. Well child visits that I find mind-numbingly routine, the "nothing" complaints that abound in the office, and general adolescent medicine in general (can't they just grow a frontal lobe already?).