I would conside that to 'doodle' is to create a picture, or drawing while doing something else, to 'scrawl' is to write something badly (but it is
words you are forming, not something abstract) and to 'scribble' is a quicker action, with no desired result (when I scribble I would make zig zag lines, perhaps to make previous writing unreadable, but I may call a child's drawing a scribble when really it is a masterpiece
)