As a child, I enjoyed visiting my cousins for many reasons, but one of them was that they had a bunch of Hardy Boys books. I don’t remember many of the stories, but I remember enjoying them. As I searched for things to read with Elijah, these came to mind. They’ve been out of print long enough that they’re all available for free download on archive.org: https://archive.org/details/hardyboys
The books have all been updated and revised to removal racial stereotypes, and the stories hold up. He loves them! We just finished book 3. I wonder how far we’ll get before I cut him loose on the rest by himself? For now I’m enjoying this as time that we spend together. Hopefully he is too.