C.A.
Hi:
We went to Kauai last November. Our children are 11, 7, and 17 months. We had a great time and it is a very beautiful island.
Those twins are going to 'ground' you though. There really are not any boat tours for kids that young. There really is enough to do though especially if this is your first time on the island.
Things that you can do successfully with your young ones:
'Chocolate' tour....this was fun, they should change the name to fruit and chocolate tour. It is kind of a granola, hippie-ish tour but we learned a lot and had fun.
Kauai Plantation train tour....you can take a train through an old plantation and try their rum afterwards.
Weimea Canyon......this is a full day's drive but very beautiful
Smith Family Luai......Very beautiful gardens; well done for as many people they are serving; and the food was great. There is suppose to be a different company that does a luai and our conceirge at the hotel recommended it but we had already prepaid before we left for the trip. Turned out just great!
Our two favorite beaches were Lythgate Park and Anini Beach. These are 'baby' beaches so the big waves are 'held' back and you can swim and play in the water.
I found plane travel to be saved by the airline attendants. One stewardess took our baby as she passed out complimentary flowers to the first class passengers.
We liked CJ's for steak and seafood.
We stayed in Princevalle; if you are not you should still drive that way and past; it was very gorgeous!
There is a company called Ready Rentals. They rent out pak and plays, cribs, high chairs, and other needed items that you don't want to carry on your trip. I found their rates good and they had the high chair and her pak and play ready before we got to our condo.
Have fun...I definitely want to go back.