|I didn't face the same problem as you, when mine were little, they didn't have cell phones, Nintendo's , (or what ever the newest version is today), no TV in their rooms, no computers, so basically , going outside to play was a treat.
As far as the outdoors, we were what would be considered upper lower class, so we didn't have an RV & barely could afford a large tent, but when we went camping they were never bored, fishing, swimming, playing in the campground all day, of course back then you didn't have to keep a constant eye on them, (no one else wanted them) :)
Perhaps, if you have the room, take one of their friends that likes the outdoors, maybe a little peer pressure.
I don't know where you live, but maybe take them someplace like Custer State Park in the Black Hills of SD, an awesome place, with all the animals.
Or somewhere like Dinosaur World in Cave City KY., or Guntown Mountain across the road where they have shootouts in the street, while not really the outdoors, it does get them out the door, and away from those silly video games, these are only a couple things, there are MANY more across the country.