I went on NCL/Hawaii last year w/my then almost two and nine year olds. Why don't you read the article I wrote, listed on the main page of the family section, titled, "Hawaii with Kids." Let me know if you have any q's after that.
Luisa Frey Gaynor
Family Cruise Editor
Sorry I don't have recommendations for kid beaches, all I can say is be very careful and do your reaserch because the strength of the ocean varies with what season your in. A calm beach in summer could be the opposite in fall and winter and vice versa. There are lots of great travel books for Hawaii that will clue you in on what beaches are suitable at the time of your visit. Life jackets are also a good idea for the kids if going in the ocean.
Hi just want to second the life jacket recommendation. We have taken our kids to Hawaii twice( land trips) and even on Waikiki beach ( which is pretty safe for kids) the surf would knock over my three and five year old very easily.
We were surprised at how many people didn't and were constantly picking their kids up , what if they had their backs turned for a minute?
Hanama( can't spell it, sorry) Bay is a good kid beach on Oahu, it has no surf, it is filled with fish to feed, and if you snorkle it is great.There is a concession , washrooms, and you can rent snorkle gear. Go early in the day, it does get crowded.
If you don't want to do the beach then go to the Polynesion Cultural Centre, even the kids will like it, it is like a living museam of of the polynesion people, we loved it, so did kids.
Kaui, has a few nice( kid friendly) beaches( south end ,Poipu)but there again watch that surf.