Marble Races with a cheap pool noodle (occupies the kids for hours.) Did this, but instead of cutting the pool noodle, the marble is small enough to fit inside the full noodle to roll down. Then can use the noodle for other things too!
Take a 2 liter soda bottle, poke holes in it. Attach to a garden hose. Toss over a tree branch and let hang for a kids water sprinkler. You can loop it over a tree branch and let kids bat it around for more watery fun!
Toss Hula Hoop Over Balloon Game: Sunshine, balloons, hula hoops-what more could you ask for? This outdoor party game combines fun and learning as it allows kids to improve their gross motor skills and basic math skills.