Thank you Susan Jones.from her Canadian grandmother! Been making for 40 years myself!
"KinderBach Piano Pals - I’m not the first to put characters on the keyboard. It’s a memory trick used by different piano methods to alliterate the letter name of the keys. I think the earliest usage was in the 1930s. However, in other piano methods the characters mean nothing more than a tool for recall in small children." Click pic to read more on the blog.