I’ll chime in with a thought. As long as the method used is sufficiently gradual, then it won’t be nearly as important as the teacher. A good teacher who understands young children will make any reasonably gradual method method work. With young children, the success or failure of guitar lessons depends on how much they enjoy working with the teacher. Although an oversimplification, Tiago’s 2010 post is still valid: “In the end there is no bad method for a good teacher and no good method for a bad one.”
I start kids with the eight notes of a G major scale. As soon as they can play this, it’s on to “Twinkle.” After that, we add a fourth string open D and tackle “Frère Jacques.” (American kids under the age of 7 might know this as “Where Is Thumbkin?”) And after that, we do Beethoven’s “Ode to Joy.”
Once my students can do these three tunes, I start them on Aaron Shearer’s “Learning the Classic Guitar, Part Two.” This book is assuredly not targeted at young children. I don’t care. My mantra is sell it and make it fun. (I get mileage out of telling young kids they’re using a “real book” that adults use, not a kiddie book.) And teachers who do their job right can sell any method of comparable level.
With young children, it’s the teacher that’s crucial. And it’s probably just as true for adults.
South Euclid, OH