"What really strikes me about this is that it's utterly symptomatic of the way that DC has spent actual decades unable to figure out that Captain Marvel is a children's character (to a greater extent than most superheroes) and ought to be written as such."

I think this is only true if you take the approach that only the "real" DC Universe counts, but those selfsame children you mention aren't going to have that kind of fannish attitude. Outside the DCU, DC's done a bunch of kid-friendly Shazam comics: Jeff Smith's Monster Society of Evil, Thunderworld, that series by the Herobear guy, the recent Convergence two-parter, etc.