Call up the nurse manager of a pediatric ICU nearby, or preferably one at the same hospital you work at (if you have one) and ask about the availability of job shadowing. You can watch and observe the day in the life of a PICU nurse and see if it's all you thought it would be.
Every nursing niche has its positives aspects (in PICU, the incontinence isn't as big, children are resilient and may improve and be a giggly little booger that just make you smile all day) and it has it's downfalls too (children die, parents don't visit or care, really sick kids may not get better).
Can you handle those events? Shadowing would be a great place to start to see if that's what you would like to do. Good luck!