Our first boredome buster was Dino Fossils from Little Bit Funky (who is doing a "40 Ideas: Activities to do with kids" this summer, she has some really good ideas already posted. Our next one from her is going to be the water balloon pinata - THAT is going to be a hit!):
We happened to have a bunch of crayola air drying clay left over from gifts Luke received long ago (if we did it again, we'd use another brand, Crayola is too squishy). And of course we're certainly not short on dinosaurs or tiny animals to make the fossils from. The boys loved this, and wanted to keep the fossils with the animals to use as a matching game. I was planning on having them just do a few fossils each (maybe 6?) But they loved it, so we made one for every animal we had, and used up our store of clay.
Secondly (and an even BIGGER hit): Straw Rockets.
I have had this pinned for a while, I pinned it myself from Ucreate, and then one of my favorite craft bloggers (I Am Momma Hear Me Roar) made them with her kids too.So a few afternoons ago, when the kids were driving each other crazy, and it was WAY too hot to play outside, we got out our paper and crayons and went to town.
This takes no time at all, involves things you're likely to have on hand, and the kids can entertain themselves for hours blowing them off straws once you're done.