This might be a little expensive for the whole family, but what an experience!!
Don't worry about missing the Heliport--it's on the main road, across the road from the ocean. Just keep a look out for their bright blue helicopters, and in case they're all out look for a big white airsock.
We went on the Big Island Spectacular--a two hour flight, we set down in Hilo for five minutes for refueling halfway through the trip. The first half of the flight was the trip to the volcano and seeing an actual active volcano. She was spewing loads of smoke, and thankfully not much else. Then we viewed Madame Pele's lava, including watching lava fall into the ocean as the Island continues to grow--more of volcanic badlands before setting down. On the return we explored the lush rainforests and the Hamakua Coast. Finally, the deep and immense tropical valleys of the Kohala Mountains, with dozens of cascading waterfalls, provide the perfect finish to the ultimate Big Island adventure. The cost of this awesome event $340 per person in the A-Star--it was a bit of a squeeze in the back with four adults. The ECO-Star is $410 per person.
Flying over the volcano and then viewing the lava trails with lava dripping into the ocean--how the island is constantly growing was phenomenal. However, a very close second was flying into the one valley, cresting the ridge, the helicopter just seemed to drop a little (this is when some struggled with motion sickness), but the view amazing of all those waterfalls.
There are several other tours including several on the island of Maui, check out the website.
For reservations I suggest calling or visiting their website, don't try turning up at the last minute.
Hint: Wear dark colors on the flight as that minimizes reflection in the window especially when taking photos.
Hint: There is a video available on landing of your particular flight for $20, however I found the quality not that great, so it's a matter of preference.
Note: A couple of people didn't altogether enjoy the flight because they experienced a couple of bouts of motion sickness. Dramamine might be the answer for you if you have trouble. This is too good of a spectacle to miss.
If you're staying in Hilo it might be easier to leave from there, I understand they do have flights from the Hilo Heliport.
They also have flights running all day, including I believe a flight at dusk/evening over the volcano which is supposedly amazing as it allows you to really see the lava trails at night. These trails are more difficult and not as inspiring during the day.