Rice 'n Beans
What you'll need:
Food coloring and vinegar (optional)
Bowls, spoons, measuring cups, etc.
I got this idea from a children's museum we visited up in Truckee. They had a HUGE table filled with rice and sand toys and my son played there the ENTIRE time we were there (and to capture a 20 month old boys attention for longer than 30 seconds is a miracle).
Take some dry rice and beans and put them in a bowl with whatever you've got (I used little cups, spoons, measuring cups and mini muffin tins).
If you want to get fancy, you can add a couple drops of food coloring to a little bit of vinegar and toss it with the rice. Lay it out to dry (I put the rice on a sheet pan) and once it dries you have some colored rice!
So easy and the kids will have an awesome time!