There are times that the lines will be short to non-existent, but these aren't necessarily your most popular pool times. During the afternoons, expect long lines. Morning when first opening (I forget what time) and evenings during first dinner seating are rather quiet. Also, port days might be slow, particular earlier - we stayed onboard in Nassau and it was great until about 2-3pm when everyone started returning from excursions. The morning of our sea-day was also a great time to do the pools and aquaduck, it got crowded around noon.
One thing...I don't recall the height requirements. Make sure both boys are tall enough so you don't end up with a meltdown onboard as you try to enter the ride. And with 2 young ones, again depending on height, you may need a second adult unless one is tall enough to ride alone. There are 2 separate height requirements - lowest is to ride at all, and a taller one to be able to ride alone. Only 2 passengers per ride.
Enjoy your cruise!