This is what we do on hot days. Stick the kids in their swimwear and get out the water! We bought this weird octopus thingy from Amazon. It basically attaches the the hose and squirts water everywhere. The kids love it, especially Tommy, who enjoys grabbing one of the tentacles and pointing it at Alice (who surprisingly doesn't seem to mind, I was expecting tantrums!).
I love how something so simple can bring the kids so much joy! Haha!