Inexpensive pool noodles into backyard toys...
Easy and Fun!
Cardboard tubes + box = hours of fun!
Exploding bags with baking soda and vinegar-science lesson. They take off like rockets!--kids would love this
ice eggs - Freeze balloons filled with water and small toys. Cut balloon off and play with eggs outside. Provide spoons for cracking ice and digging treasures out. SUMMER
This site has really hilarious game ideas for adults and kids.
Balloon ninjas to shoot with nerf guns.
Camp Mom! 20 Activities to Make Summer Awesome
Minute To Win It games - For indoor recess, this is a must!