Your daughter will definitely like the pool at Kings’ Land. That would be my first choice of TS for the West side.
HVNP is really best done on your own with a car… the Volcanoes Nat Park website has lots of info for organizing your visit there. Not to be missed, IMO: doing the Kilauea Iki Trail, visiting the Steam Vents, the Lava Tube, the short walk to the caldera overlook near Devastation Trail, and the drive all the way down Crater Rim Drive to the Holei Sea Arch. The whole park is very unique and awesome!
We usually devote a day and a half just for the park, so an overnight at Volcano House or one of the several properties in the Volcano Village itself would be called for. Your initial thought of flying into Hilo from Maui is a sound one, then out of KOA.
What I would do is try to schedule a flight into ITO, so that you can pick up the car, have lunch in Hilo, then head to HVNP. Drop off your bags, then stop at the Visitor Center to orient yourself and figure out how to spend the rest of the afternoon in the Park - such as driving down Crater Rim Dr... Plan on having dinner at Kilauea Lodge or Volcano House. If the eruption resumes and there’s red lava visible in the crater, then you can go back in the Park to see the glow.
The next morning, I’d do the Kilauea Iki hike first thing in the morning, then head back to Hilo. Either spend a bit of time sightseeing in Hilo, or head straight to do the Northern/Hamakua Coast route. Stops enroute could include Akaka Falls, a vanilla farm near Honoka’a, getting malasadas at the Tex Drive-in, and making a brief stop at the Waipi’o Valley Overlook. Driving through Waimea, you can make a worthwhile stop to buy groceries at the big Foodland or KTA stores before arriving in Waikoloa.
An interesting sightseeing combo is to also visit the Tsunami Museum in Hilo, with a brief stop in Lauphoehoe where it hit on the Hamakua Coast.
Hope this gives you more food for thought for your planning.
