Character Analysis
At first, Leo's parents seem like totally normal, hard-working people—probably not that different from your own parents. The revelation that they kidnapped Leo and put him in their dead son's place certainly complicates things, doesn't it?
But you have to remember that Stepan and Anna lived through some rough times—and we mean really rough. Those years of conflict and famine affect each of the novel's main characters. For example, Leo's birth mother Oksana spent "every waking hour and every fretful dream" worrying about how to keep her family together (1.1.5). Stepan and Anna suffered greatly during this period too. After all, only desperation could lead this mild-mannered couple to go hunting for children to feed their sickly son.
(By the way, do you think the Soviets acknowledge that there were famines going on in the country? Spoiler alert: nope.)
Things don't go according to plan, though. Their son—the original Leo—died while Stepan was bagging Pavel, rendering his huge personal sacrifice worthless. Though they offer to free Pavel, the boy has lost memory of his home—and things aren't going very well there, anyway. That's when they do something incredible and disturbing: they feed him a soup that surely contains the flesh of their son, "offering their own flesh and blood" to this stranger (4.44.31). Once again, they make another huge sacrifice in favor of survival.
It might be tempting to get all judgmental about this, but we'd warn against it. Few of us have lived through times as unforgiving as Stepan and Anna have—you never know what you'd stoop to unless you've experienced it. Though no one can dispute that they did some pretty messed-up things, they did their best to rectify their mistakes by raising Pavel as if he was their own son, in the process forming him into the sweet bro we meet in Child 44.