I'm a PICU attending and every children's hospital I've ever been at, the peds uro group is always very busy and seems like they could use more staff. Where I did my residency, they had one full time peds uro retire (other staff were just part-time) and took a while to find that replacement and the only way that guy caught up to the backlog of cases was to be in the OR 6 days a week for like 8 months.
If you want to plug yourself into an existing infrastructure of a children's hospital, then yes, like nearly all pediatric fields, it's more geographically limiting, This is especially true if you want to really focus on the higher complexity cases where the child also has a plethora of other pediatric subspecialists. But, if that doesn't appeal to you or you have location considerations that don't involve bigger cities, I think if you are satisfied with the bread and butter stuff with less frequent complex cases, you could probably carve out a satisfying practice in any population center with a higher acuity NICU that has reasonable volumes. For example, I used to do PICU locums in Evansville, Indiana - which is a town of about 125k, and is smack in the middle, 2.5 hours away from St. Louis, Indianapolis, Nashville and Cincinnati. It has a big enough NICU that would provide a good starting base, and you could readily attract patients by saving parents the hassle of having to drive to the big cities. Similar sorts of communities could be found with a little digging.