The Aston property is the Colony Villas (also managed by other companies, in addition to VRBO); quite nice, pretty much like the other condo properties in Waikoloa. Waikoloa Beach REsort is a very good base for seeing the rest of the island, puts you nearer some very fine beaches (Mauna Kea, Hapuna, etc.), and there's a grocery, fast food court, and shopping at the entrance to the resort complex. A-Bay is pretty nice for snorkeling and swimming, too, if you don't feel like exploring (free public beach parking between the Queen's Mall and the Marriott, complete with facilities). A good choice!
p.s. the jury is out on the efficacy of 30, 50, or even 100 SPF sunscreen, esp. combined with water exposure; best bet is to protect your kids by having them wear light tee-shirts, even (especially) in the water, and hats (in addition to screen).
Don't miss Akaka Falls north of HIlo, and walking through Thurston Lava Tube (steep stairs down, piece of cake back out) at Volcano National Park is fun. There's also a free zoo in Hilo with a white tiger (refugee from Vegas) in his own nice green enclosure; the grounds are really pretty, and they have primates and exotic birds in outdoor cages, too.