The majority (I don't know the %) of fellowship trained peds anesthesiologists practice in a children's hospital setting because that is where much of the pediatric acuity and complexity resides, also often a program designed around children, a community of peds anesthesiologists to work with, etc. etc. if you liked kids enough to do a fellowship, then presumably you'd like to spend the majority of your OR time taking care fo them-- of course there are exceptions, those who do peds anesthesia fellowship so they will feel comfortable taking care of any child at any time.
I don't see peds anesthesiology being as affected by CRNAs as general adult anesthesia, particularly in large children's hospitals with critically ill neonates and children, but I don't have a crystal ball. I feel pretty confident in the short and probably long -term of job security as a pediatric anesthesiologist as long as I'm in a hospital with a Level III NICU and a PICU.