Update: I read the book for my son's class and showed them Music Blocks. The first-grade group listened very well to Ada & Zangemann, and they enjoyed creating some visual code together, reading the scripts on the screen, trying to predict and watching the results, and, finally, remixing the code.
I reminded them they can remix and share their new project.
And, of course, since Music Blocks is AGPL, they can use, share, study, and remix the whole programming language, if they like!