This is a book for teaching young kids. Trying to start them off with a language like Java or C# would be a terrible idea; not because they are bad languages, but because they have such a high learning curve.

With something like Ruby we can start the child right off with

puts 'Hello World'

Immediately they have a positive feedback cycle. At this stage they don't need to know that a top level object has been implicitly created for them and this statement is part of that object. We'll get to that stuff later. Start off basic with some simple lines of working code. Move up to conditionals, loops, add in methods later in a sort of procedural fashion. Eventually higher level concepts will be introduced.

Also to this point of yours, "It doesn't have first-level functions, instead it has blocks (which can take parameters to serve the same use as functions but aren't)."

That is one of those things that comes from someone that hasn't spent enough time with the language. While the treatment is slightly different, the outcome is the same. Ruby supports closures and passing methods to methods.

Before you retort with, "But blocks/procs aren't 'really' methods", you might also want to step back and realize that Ruby also allows any method to be passed as well using &Object.method(:method_name); that basically says "Oh hey; pass this method just like a block".