I get it. Yellowstone with my young kids was seeing all the attractions.We're already:
Spending a week in the Eastern Serrias with my family
5 days on the East Coast
River trip
Backpacking trip
I get that trips are cool. But I'll counter, and ask why? What is going to make Iceland cool with your family? From my experience when your kids are young it's just about doing new stuff together, which can totally be cheap and local. As kids get older, and they've already acquired an amount of experiences, good and bad, and they're capable of actually engaging in a place, then it's the time for extravagant travel. I'm not there yet, another couple of years.
It's like... You don't waste good wine (or whiskey) on a 21 yr old. They're not capable of appreciating it yet. That's the same approach I take on vacations with the kids. When they're in HS and college I'm sure we'll go all over. But not now.
Yellowstone with my grown kids was three days of good fly fishing, drinks at the hotel, rodeo in Cody (I know) and good stories over camp fires.