Or it could be read one per year?? A seven year old would probably find Harry Potter a challenge... So it’s something that a parent and child could read together... Four or five pages before bed a night perhaps??
If I enjoyed a series (even as a kid), I don’t think I’d wait a year for the next installment if it was availalbe now. I don’t think seven-year-olds would have too much of a problem with the first book other than its length. It’s very big for a first or second grader. Second graders start reading more chapter books, but Sorceror’s stone is a pretty long book by that yardstick. On the other hand, in the first book, many of the chapters read like little mini-adventures on their own. That was the one thing that amused me about the story: what I thought was just going to be a series of misadventures in the school all tied together in one way or another at the end of the book. She got me.