by Gertrude Chandler Warner
This one is much shorter than the first three books. I remember reading it as a kid, but it felt a lot longer and more mysterious back then. It could have done with some rounding out, more about Aunt Jane and the ranch perhaps.
The Boxcar Children = most read series between the ages of 6 and 9 for me. I think of these fondly. Every child should read this series.
Good for young readers.