I taught piano lessons and discovered the following.

There seems to be a break around 8-9 years old (or when the child starts to read). Before that age, all learning is imitating; after that age it is more cognitive. (Someone told me that children in countries other than the US are not forced to read at a young age and have less reading problems as they grow older.)

I enjoyed the Suzuki method for young children. (Yes, it's for the piano as well as violin). I can just see Ella with her little guitar just like the Suzuki kids with their little violins. I wish every student could benefit from this method, but the one drawback (a big one) is that it requires tremendous input from a parent. All practices involve parental participation. The nice thing about this method is that the very young child plays "Twinkle, Twinkle Little Star" in a sonatina style and sounds really grown up. It gives them an ear for hearing classical music, and the imitation allows them to play and experience music without having to read. Sounds like you're already doing this with easy-to-play songs. Also finding songs which little hands can reach is important. Other methods use lots of duets (the teacher plays the difficult part), and the resulting participation is fun for everyone.

I think both you and Callie have found the ways to let the child participate and make music!

Mary