I see that my question has caused a lot of discussion. Yes, the text makes it clear that they are orphans. They are definitely not pupils, as this term is used for younger ages. The text goes on to say that these 15 year olds just had a child themselves even though they are still teenagers. So pupils is inappropriate. "Residential school" is not politically correct at all. I am Canadian and this term evokes very negative connotations. (see the following link for why
http://en.wikipedia.org/wiki/Canadian_Indian_residential_sch... As the text is meant for an international audience, I will avoid using this term. I like the term "boarding school" better.
I have thought about this at great length and have decided it's best not to try to translate воспитанник directly, but rather say the following:
"Polina and Oleg are both 15 years old. They live and study at the Safonovo boarding school."
The next sentence after this goes on to say that they just gave birth to a daughter.