My advice...
Don't consider an N-600 if you care about the speed of processing. Get your kids passports first. That way they have proof of US citizenship reasonably quickly.
The Citizenship Certificate that results from an N-600 application is useful once your kids leave home and need to have proof of their American-ness without tracing back through your natz cert.
So, get the passports first, then submit N-600s and don't bother gettting worried about how long they take
(We submitted my daughter's N-600 in Dallas almost a year ago)