We have 2 boys - 5 year old will be on his 10th cruise in Jan and 21 mo old will be on his 3rd in Jan.
Our biggest "hack"? Sail with the grandparents! LOL! We find that it helps to have the adult to kid ratio higher.
We always take a bag with small toys, coloring supplies & story books for playing in the cabin. Usually take a coloring page and a couple markers to dining room for the 5 year old. DH usually takes the little one for a walk after viewing the menu while waiting for the food to arrive. We take one of those over the door shoe organizers with clear pockets - can be used for anything from hair products/toiletries to socks/shoes or toys, sunglasses, etc - really helps with storage space because the cabin seems to shrink with more people in it. Don't forget the hats & sunscreen!
Cruising with kids is different than without and you may have to take turns doing things in the evenings while one adult stays back at the cabin to put the kiddos to bed. But it can be a great family vacation. It's all what you make it!