Cool the kids off with a homemade sprinkler. Take a 2 liter soda bottle, poke holes in it. Attach to a garden hose via a male to male adapter that cost less than $5 at Lowes. Toss over a tree branch and let hang.
Build your kids their very own tire seesaw! http://diyprojects.ideas2live4.com/2016/03/01/build-a-seesaw-from-repurposed-tire/ This DIY project is a very great alternative to the usual, metal seesaws you can buy. A tire teeter totter is light and movable so that you can easily relocate it if you need to! It can also be customised to suit your child's personality. What's not to love? Do you know anyone who would love this idea, too? :)