How about we move this to the PICU forum where it would fit better?
I can't speak for other PICUs but I know that to work in ours, you just have to apply. Seriously.
But I think you're more interested in knowing what qualifications would make you a good fit in PICU. So these are some that I think are important...
a good grasp of growth and development
knowledge of pediatric norms in vital signs, labs and basic drug dosages
excellent assessment skills and finely tuned instincts
flexibility and creativity (think out of the box)
the ability to translate complex concepts into simple terms that even the child can understand
the ability to not take things personally and to collaborate with people who don't have the same body of knowledge you do (allowing a parent to make choices that you might not agree with but that will not harm your patient, for example)
a strong sense of oneself and how one's coping mechanisms work (if you're going to cry for a week every time a patient dies, then this will be a very hard place to work.)
A basic critical care background can be adapted for PICU without too much trouble. It's the psychological aspect that many find hard to deal with. There are days when it's an absolutely miserable place to work, and others when it's so great you'll wonder why it took you so long to come aboard.