There are plenty of more constructive, yet still fun things they can be doing with their oodles of time. :)
A little while ago, my kids came up with something we like to call "Tunnel Bowling". It's such a simple thing, but they literally spent an hour or more playing it.
Just grab an old box (the longer/taller the better), or in our case a chute that goes to a kids' play tent, set up your pins...
and knock 'em down!
If you don't have an old box, move the kitchen chairs away from the table and use under the table as your "tunnel". Or line up some kitchen chairs in a row and bowl between the legs of them.
We purchased the Little Tikes bowling set a while back at Toys R Us. If you don't want to buy a set, you can get creative with light, non-breakable objects to set up for "pins" and simply use a heavier play ball.
Looking for more summer activities to do with your kids that don't involve technology?
Check out this list of "20 Fun Summer Activities for Kids"!