We live on O'ahu and went to the Big Island last Christmas. We stayed at the military cabins, so I can't really help w/ other accomodations, but from what we saw, The Volcano House ( I think that was the name of it) looked decent, but most of the motels in Hilo and surrounding areas looked a little

to me. We only did the east side of the island to include Pahoa, Puna, Kapoho, Hilo...We never felt unsafe or witnessed any crime. We did have a rental car but left NOTHING inside each time we got out and we never left stuff in the trunk or opened it and put stuff in while we were in a parking lot. Puna and that whole area is very tropical/jungle-like, so the views were great. I will tell you that Hippies didn't not die out after the 70's though...they all moved to Pahoa..lol!
You can also stop by the Mauna Loa factory on the way from Volcano to Hilo. Very small production, but you can do a self-tour and watch the nuts go from shell to chocolate covered...the kids thought it was neat and it doesn't take long at all. The products inside are expensive, but you can get the "ugly" chocolate nut clusters for a good price and IMO they taste better than the "pretty" ones.
The Volcano Nat'l park was great. Check out the steam vents, Chain of Craters road, Thurston Lava Tube(take flashlights if you want to go further into the cave..the "tourist" section is lit well enough, but after that is goes black and you can't see anything). Haleamaumau crater is neat, but if you have small children make sure they have something to cover their mouth/nose with b/c the sulfur is very stinky and caused both of my kids to cough pretty violently and we had to leave.
The Petroglyphs are neat to see as well and are located off the chain of craters road..it's about a 3/4 mi. hike over lava rocks to get there. There is a little bit of a path but definately NOT stroller friendly.
I think you can actually see the lava if you hike down to it. When we were there it was only visable from a helicopter and wasn't running into the ocean.
If you have a 4x4 you can drive up to the very top of Mauna Kea...the road is a little hairy though. If you go at the right time, you can see snow on the top. DH has been up there, but we didn't go up there as a family due to our rental car and they didn't recommend kids under 16 go up b/c of the increasing difficulty to breathe the higher you get. We did stop at the visitors center halfway up and it was COLD! Kids drank hot chocolate and we got to see many people that had their personal trucks full of snow.
O'ahu..can't help with places to stay, but the Oahu Revealed book is great and can give you some recommendations...we always stay at the military hotel, Hale Koa, right next to Hilton Hawaiian Village. That is a great hotel in a good location, but it can be pricey. Souveniers can be purchased at
Walmart like someone else said, but you can also go to the Aloha Stadium Swap meet on Wed, Sat, and Sunday and get those along w/ Hawaiian foods and other things for sale pretty cheap.
Nuuanu Pali lookout has great views and is VERY windy. Check out the Blow Hole and Hanuama Bay if time permits. Kaneohe Bay, Lanikai, and Kailua beaches are GORGEOUS. Sharks cove on the North Shore is good for snorkeling and you can often see turtles on the first beach you come to after you leave Haleiwa town. Waimea bay is great as well, but parking is horrible...you can park across the street at the Waimea falls park for free and walk back to the beach if you can't find closer parking.
Paradise Cove is my favorite Luau...Fabulous sunsets. Polynesian cultural center is neat too, but they are alcohol free and it can be an all day thing. Paradise cover is only a few hours long at night...pay for the package where they bring you the food instead of having to get up and get your own food from the buffet...it is worth it. The seating is MUCH better and you don't have to deal with the insane lines and crowds around the buffet.
Ala Moana mall is nice...food court is very large and has everything from Hawaiian food to your basic pizza meal.
I'm sure I'm missing things, but the Oahu revealed book will help you greatly! We are a military family and have lived here twice, and we still use it all the time to find new places to eat or new adventures!