It doesn’t look like there’s a thread here for this, and it seemed like the place, so I thought I’d start one, and both propose the creation of a new tag and nominate a story to receive it.
I know the site preference for tagging is to use existing tags, instead of creating new ones. (Something I wholeheartedly support.) And I’m not the actual author of the story in question, so my opinions on how it should be tagged are just that: My opinions.
In that kind of situation I prefer to run ideas up flagpoles, rather than just launch into them on the strength of nothing more than my extremely limited viewpoint.
Soooo, anyway, I wanted to suggest the new tag: infantilism.
Which isn’t quite “age regression”, and isn’t quite “mental regression”, and isn’t quite anything currently listed in the tag cloud, IMHO (though it’s a cousin to several existing tags).
As an example of content the “infantilism” tag would describe that no existing tag quite covers, see Willie CiCi’s recent “The Apartment”, primarily on the strength of the ‘baby-talk’ scenes.