On our visit to the Big Island of Hawaii we stayed at Halii Kai at Waikaloa which is more of a vacation rental with separate bedrooms, living space, and kitchen. Kitchen of course is convenient for cooking and families. Their Ocean club area has a pool and hot tub that overlooks the ocean.
Of course the top most visited location on the Island is Volcanoes National Park with one of the largest active volcanoes on the planet named Kilauea. We ate at the Volcano House which provided quality food and an amazing view of the active volcano. We then proceeded to explore the park and got a closer look at the outlook and then walked through a lava tube
The best beach that we found was at Waialea bay. Less crowded and tons of shade. The water is aqua marine on both ends for swimming while the middle of the beach has shallow rocks and a natural breaker great for snorkeling.
The best location for snorkeling for families has to be at the Hilton Waikaloa village where they have a natural salt water lagoon. Safe from rough waves and life jackets available, turtles and a variety of marine life frequent here all day including jumping fish that will jump right into you. The lagoon is free to use if you stay at the Hilton hotel or sister locations, however you can purchase a day use pass for $100 per person.