I did some babysitting not that long ago. I knew it was going to be several hours long, so I tried planning ahead--I didn't want them to sit the entire time in front of the tv, but I also knew that they wouldn't play outside the entire time (it ended up being about 6 hours). I also had things inside that I still needed to do. So I came up with a quick, easy craft that all the kids could do and then play with.
These two (above) were done by the 2 and 3 year old. The three (below) were done by a 4, 10, and 7 year old.
They spent about a half hour on the paper bag monsters and would have kept going if I hadn't needed to start making dinner. The paper bags are just the sandwich bags you can get at the grocery store (less than $2 for 50 of them). I had pipe cleaners, glue, crayons, markers, paper, safety scissors, tape, and googly eyes on hand already.
So give it a shot! Get some bags, put them in front of your kids with supplies, and let them at it!