Carving out time to work this summer has gone so much more smoothly when the kids know when to expect "fun time". We go to my parent's pool once a week. Then we plan one other day where we will go do something away from the house. Whether it is a park, zoo, museum or beach. You don't have to stay long, I found a good 2 hours of unadulterated fun wears them out good. You may even get a nap out of the older ones and find some work time for you.
Each Monday morning I announce to the kiddos how the week is going to go, what day will be our "fun day" and what we will do. Then when the "i'm bored" comes out I can point to the calender and remind them of what is coming.
On the days when there is no "fun" planned, it is still important to spell out what is going on. Let them know when you will be working and what will be going on when you are done. (sprinkler, playing outside)