Hm... First off, call it 'programming', not 'coding'. I dislike the word 'coding' in a didactic context, since it implies what you're doing is enciphering something. That's the exact opposite of what a skilled programmer does, which is to try to write a program in the clearest way possible.
The only other thing to realize is that most programming languages kind of start with algebra as a basis. When you do "a = 42", that's kind of an algebraic concept, one that might not be suitable for an elementary school student, just do to their age. If you choose to do Ren'Py, then focus on the non-algebraic portions - basically, the control flow bits - Apart from dialogue and scene/show/hide, maybe focus on labels, menus, and jump, but avoid things like screens and complex logic.
I'll also take this chance to plug the LOGO programming language:
http://el.media.mit.edu/logo-foundation/ LOGO is a language based on turtle graphics:
REPEAT 4 [ FD 100 RT 90 ]
Draws a square on the screen. It was designed to be suitable for young children because the directness of turtle graphics tends to avoid the abstraction that I think you really need to get algebra to understand.(I don't know scratch well, but I think it might be the same way.)
Fundamentally, though, the thing young programmers need to learn is to see the computer as something understandable. That it's not some sort of magic box created by the high priests on mount olympus, but that it's just something people like you, I, and them program. Chances are most of them won't go into programming as a profession, and that's fine. But if they see computers as a tool - that's valuable.