You probably have some worms in your garden and you and your son could attract them. Just place a piece of corrugated cardboard on the ground, preferably where it is in contact with the soil. Water it well and leave it nice and wet for 24 hours. Then flip it over and you should see some worms! The little red ones are the ones used for kitchen composting or vermicomposting in a plastic bin with holes. Catch them fast as they don't like the sun and will try to wriggle into the ground as quickly as possible. I have done this myself and gathered five or six worms every day. I have also heard that sprinkling any kind of grain under the cardboard makes it super-attractive for worms, but haven't tried that.

Try posting on the vermicomposting forum and see if there are any GW members who live in MD (or VA/DC) with extra red wrigglers to share. I remember coming across a thread from several years ago in which members were sharing and mailing spare cocoons and red wrigglers to others in their geographic area.

Here's my two cents: locate a bunch o leaves (enough to fill a trash can) wet em down and leave them alone for a month or two (wetting em down if they do happen to dry out) after a month or two you should have a few compost worms that will breed like sailors on shore leave.

the easiest way to identify them is they'll have a touch of yellow on their tail ends and they will have faint but noticeable triangles running down their backs, they'll be no more than two inches long and barely fatter than two tooth picks side by side.

if you plan to attended the spring plant swap @ garden grandmas I'll try to bring some along. you can also find them @ any horse stables if you know where to look such as in the old manure piles.