I work in a CV (CT) peds ICU and we use Precedex (dexmedetomadine) quite frequently on the hard-to-sedate post-op children. We're a large center on the West Coast and do a lot of cases. I've found that when titrating up - even quickly - that the bradycardia issues aren't such a big deal. When they're super-agitated with HRs 180+, the effect isn't very noticeable. I will say, though, that it isn't the first line drug of choice for most patients.
We're currently working on a sedation protocol, and I believe that it is written in the "staged sedation" for post-op day 4 or 5 if the typical morphine/ativan +/- fentanyl aren't working.
For what it's worth, I've had only the best experience with Precedex. Especially considering that you can extubate on Precedex, it helps get through the critical/dangerous intubated periods. Look up some of the clinical trials - the drug is associated with fewer ICU days, intubated days, and shorter hospital stays in general. There isn't much that's peds specific yet, though, and that's saddening
Hope that's helpful for you!