This is most likely because so much is written about Stalin's 30 year reign that his early biographical information gets buried by other scholarly work.
As you might guess, Stalin (real name was Djugashvili) did not lead a normal life, either as a child or an adult. His father was a pretty strict and unforgiving man, an alcoholic who could be very violent against Stalin's mother and siblings, as well as himself.
He suffered other hardships too, including serious injuries in accidents, but was educated on a scholarship, and at one time (if you can believe it) considered becoming an Orthodox Priest. He was married perhaps as many as three times, and at least twice, and he had numerous mistresses, so we don't know for sure how many children Stalin had. His eldest son attempted suicide, but he didn't die. He was later captured by the Germans during World War II and Stalin refused to trade for him. He committed suicide in a German concentration camp. His second wife shot herself after an argument with Stalin, though there were rumors he might have killed her.
The links below are pretty good as references.