Natasha was raised by Winter Soldier and spent childhood in and out of cryosleep -- *found!
I've been looking for this for over a month and got no answer yet to an earlier post, so I'm trying again. Natasha was raised by the Red Room and was allowed to go to school with the children of Party officials because of her father's status as the feared Winter Soldier. Like Bucky, she was in and out of cryosleep and aged at a much slower rate, with her father right there everytime she was awakened. Bucky broke conditioning enough to realize that Natasha was in danger of being "retired" so he took her and escaped to a secluded area (a wooded part of Europe?), teaching her more survival skills and how and when to kill to stay alive. (Sorta like the 2011 movie Hanna.) Natasha get the opportunity to emmigrate to the US and reluctantly leaves her father behind. He makes it years later when she's a part of the Avengers.