The missing frogs are here: Frog Forum - Froggies - Blogs

I agree they are Northern Green Frogs, Lithobates clamitans melanota. They're too young to sex though, the tympanum is only larger than the eye on adult males.

For future reference, here's a list of frogs and toads found in Maryland Discover Maryland's Herps - Wildlife and Heritage Service - Maryland Department of Natural Resources