Here's something I figured out last summer: go to the park early, right after breakfast, for a little while. It's not hot, it's not crowded; it's actually quite pleasant. I'm going to try to take the kids once a week during the summer.
We also enjoy taking walks first thing in the morning. The big kids have been rollerskating for our walks lately while I push Baby in the stroller.
Once we all went out to the backyard before breakfast and I weeded a third of the garden while the kids played. I should do that again with the other two-thirds of the garden.