Ask HN: Introductory programming books for a young kid?

I'm looking to purchase a belated Christmas gift for a nephew of mine in the form of a programming book. He's had some experience creating games with drag and drop logic using Scratch and is now looking to transition into using Unity. However, I believe it would be best to give him an introduction to programming in general before he takes that step.

He reads at about the level of a 12-year old, is very comfortable using a computer, and picks up new concepts very quickly through application. I believe something that emphasizes visualization in its coding examples would be well-suited due to his interest in game development.

Does anyone have suggestions for books that would help him begin his programming journey?