"former" Eastern Europe? Did it move?
anyway have the kids parents talk to the U.S. embassy. Meanwhile, you should talk to the hospital you want to take him to. I would imagine both of those would be good places to ask. Explain what you want to do, and ask how to start. Another good place would be that country's embassy here in the U.S. Or maybe the travel bureau? I found this:
travel.state.gov/content/travel/english.html which might have some useful information. Honestly, this is probably better directed at people who are familiar with international travel. Maybe a travel agent? If you're just gonna bring him for treatment, it should be a fairly routine thing. If you're wanting to have them immigrate, then it's going to be more complicated, but I'm pretty sure the U.S. embassy is a good place to start for that, too.