I grew up poor, with a working mom.
From first grade, she had me walk from school to the nearby library, to wait there for her to get off work and get me. For three hours a day, I had nothing to do there except read and do homework. I read all the little children’s books there by the end of the first six months, the junior books by middle of second grade, and was reading adult level books by third.
Why did 19th century kids have such a superior reading level? No electronic entertainment.
What you described is unschooling: You had nothing to do. You were surrounded by books, so you read them.