I'm trying to teach Morse code to my 10 year old kid and his friend. Even setting up soon to be modified CB radios for them to do it over the air. I'm actually testing out an antenna idea today at his friend's house.
I am now a teacher, and the task you describe got me thinking. It would be tempting to teach the association of letters with their related visual patterns of dash/dots. However, a 10 year old might do better if they learned the sound-forms of the letters as discrete entities, in the same way that they leaned the shape-form of the alphabet.