Sean, there are good recommendations above. A lot of options require a fair amount of driving so maybe plan for things in town or near town ahead of the race. Then take the longer trips post-race.

If you want to see Hilo or Pahoa I’d recommend using the saddle road. The only reason to take the highway south out of Kona is to see South Point or Volcano/NP.

I don’t have kids and only made it to Hawaii once as a child. My brother and I had the best time on the Big Island because of the snorkeling. If your boys enjoy this check out Kahalu’u Beach Park at the south end of Ali’i. There is a small sea wall protecting a lot of the snorkeling area and entry/exit is easy from he beach.

We visit there all the time now, but early on we relied on The Big Island Revealed guide book. I think the format would be perfect for you and your wife and boys to flip thru and pick things to do together. It was just updated in May 2019: https://www.amazon.com/...ding=UTF8&btkr=1

Hope this helps!