Have you used this on actual kids? I feel you would learn very quickly from them.

As an adult, I can only speak for myself, and although this is nice, I think it is comparable to the functional programming programs for adults out there (for instance, Microsoft's online F# tutorial, or Coursera's Scala tutorial). The pictures and things aren't making it easier for me. I don't know if it will be different for kids.

I have went over this tutorial with my kids (12 and 13 years old) and they enjoyed it a lot.

That's great.

Did you try the regular "adult" tutorials with them? It would be interesting to see if they liked this more, or found one of them interesting.

Functional programming is already extremely abstract, and children (and many adults) have a very difficult time with abstraction. You should find a way to make these lessons into some sort of story. Perhaps each chapter contributes to some overall program. All the abstract math-for-math's sake will be REALLY unappealing to most children, guaranteed.

Completely agree. Its easier for kids to learn through stories and examples that accompany the story.

One fundamental aspect of functional programing is that it specifies the use of functions as arguments.

I like the chapter suggestion. Maybe each chapter builds upon a function that the kids can relate to. The subsequent chapters can use the previous functions as "arguments" or objects so that they understand this concept.

define kid

strong math knowledge needed to understand it. polish notation could be also confusing.

I have always found polish notation simple because it is so consistent.

The problem seems like the problem with Clojure (instead of say Racket) would be the uninformative error messages.

One problem is that kids, at least in the UK, are taught to say "one plus one" not "plus one one".

Sure, but when I was new to Lisp, I mentally read it as "add one to one". The first element of the expression is a verb, not a preposition.

This might be good thing to discuss in a tutorial aimed at kids.

My kids get very easily used to the lisp notation where the operator is always on first position