This Hawaii Island, nicknamed "Big Island," is a giant among spectacular tropical islands -- and not just because of its size there are lots of exciting sights for kids 5/12 and yourself that include dolphins, colored beaches, an active volcano and helicopter rides.
I strongly recommend a Blue Hawaiian helicopter tour, although expensive it is the thrill of a lifetime - Hawaii Island, http://www.bluehawaiian.com/bigisland/
For families my favorite snorkeling beaches are Waialea Beach ("Beach 69"), Kahalu'u Beach, and Honaunau Bay ("Two Step"). On our last visit we swam with Hawaiian green sea turtles at all of these beaches, and at Two Step we swam with a pod of spinner dolphins (including babies)! We encountered the dolphins in the wild without a tour guide, and we weren't even that far off shore! We also loved doing SNUBA (a cross between snorkeling and scuba diving) in Kailua Bay. There is also parasailing with UFO Parasail in Kailua Bay and had a thrilling time. We found that Hapuna and Magic Sands were the best beaches for body boarding.
We enjoyed seeing Hawaii Volcanoes National Park and the Thurston Lava Tube, although we didn't have a chance to see an active lava flow. Make sure to contact the park about lava viewing before you make the drive down there, because most of the time the park rangers keep visitors from getting too close to the lava.
We had a great time on the northern end of the island. The Pololulu Valley Overlook was breathtaking. We hiked the Puako Trail to view the petroglyphs, and if you go make sure to take plenty of water with you and try to go in the morning when it's cooler. It was a great history lesson for our boys and sparked their imaginations.
We enjoyed a luau at the Kona Village Resort and thoroughly enjoyed it. Our kids even tried the poi and loved the taro chips!
Another cost but the best anywhere (I have been to twelve places around the globe!) for the entire family is Dolphin Quest @ Hilton Waikoloa Village
425 Waikoloa Beach Drive Waikoloa, Hawaii 96738 (808) 886-2875
Dolphin Quest Featuring one of the world's largest natural dolphin habitats in the world, Dolphin Quest has programs for children 5-12 about 5 years ago