One way to handle that chronic complaint of “it’s too hot to play outside” is to let the kids play in sprinklers. A Slip N Slide and other such toys can work too. Just give them the chance to get soaking wet.
Kids can be pretty funny about playing in sprinklers. Some find the water way too cold, while others don’t care. But if you try to turn off the water before they’re done, they get pretty upset.
Oh, and remember to have towels where the kids can get them without dripping all through the house. This doesn’t always work – mine are as likely as not to lay their towels out under the sprinklers and lie down, but that just means I get to tell them to stay out until the sun dries them enough.
Make sure you pay attention to any water use restrictions in your area. Areas suffering from low water supplies may not be the best for encouraging the kids to play in sprinklers.