This headband holder from FunnyGirlDesigns - I think my girls could attempt to make something similar, AND it would solve our massive headband storage problem. In theory.
Make bouncy balls, as shown at Curbly - because that's just cool:
Get Trevor to make a Skateboard Swing, like at CedarWorks:
For a summer project, make a ton of Tin Can Windsocks like Random Thoughts of a Supermom:
Make tons of puzzles and then put them together again and again... see details on the picture puzzle at Impress Your Kids:
Tell the kids what a Lava Lamp is, then make one - like S.L.Smith (I don't know why this picture got squished!)
Make Marble Races, then maybe they'll play with them for hours... tutorial at A Girl and A Glue Gun:
Picnic at the Drive-In - cutely seen at Oh, Hello Friend - I can only do the drive-in every other year or so, so I guess I have to go this year...
Glowstick Ring toss - - this has GOT to be fun! Over at Momma Did It:
Martha Stewart shows how to make Pipe Cleaner Creatures:
First, drink a lot of pop - then, make a Pop Tab Headband like at Hairstyles for Girls: