There are lots of things to do around the house. Make a list with your kids one night. Include fun things like make s'mores in the microwave, have a famiy movie night, catch fireflies. It's fun to have something to look forward to, so mark these on the calendar.
In between, try home made play dough, word searches, treasures hunts in or around your house, playing outside in the sprinkler or going to the pool.
Also, consider signing up for a summer reading program at your local library. They usually give prizes for reading a certain about of books, give out weekly coupons, and its a great way to keep your kids reading during the summer. While there, check out their other programs, like story time or craft time.
For more summer activities check out my article, How to Entertain Your Kids During Summer.