Diamondback terrapins are a little different than most freshwater aquatic turtles because they live in brackish water. They are also one of the most protected turtles in Maryland. It is illegal for any regular person to have eggs or babies or an adult for that matter. I suggest contacting MATTS (based in Baltimore) or a local wildlife rehabilitator. MATTS would know more as they are just turtles. Their web site is
http://www.matts-turtles.org/Like most aquatic turtles, baby terrapins basically just want to eat small live animals like aquatic insect larvae or blackworms. They sell those at Aquarium Depot in Randallstown.
Terrapins won't eat Tetramin fish food. They need something moving. Newly hatched babies can go weeks without food as they're still living off of their yolks.
My baby turtle page is at
http://www.fishpondinfo.com/turtles/hatchling.htm but is not specifically geared towards terrapins. The care is basically the same except that they need brackish water (more salt).
Good luck!