I have seen info on making a worm farm in several places. One day while playing out back, we found several worms. I told the kids we would go make a worm farm so this was what we set out to do.
We used a plastic tub the size of a shoebox to layer our sand and soil. I discussed with the kids how a worm's job is to mix the soil. After a little more digging, we were able to collect 10 in all. It was lots of fun!