I mean, that's unrelated to the child model thing. And the idolization her classmates indulge in isn't too out of character imo.
Idolization is not bad by itself because yeah, is a perfectly normal way kids act at that age. The issue comes on the way is contextualized by Ririha's behavior. If she weren't so devoted to the gig (think on Hina's reaction to her own modelling career) it wouldn't be as jarring.
Also, I dunno if you recall being a child but when I was one there were a lot of kids who tried to fake as tho they had more experience with things than they did or knew more than they did or were more mature than they were. I don't think Ririha has any intention of taking things to a sexual level. Her seduction is just emphasizing her cuteness after all. To her understanding a lolicon may just be an older person who is attracted to kids, without any awareness of all the gross awfulness that may entail.
You're right and Ririha probably isn't trying to take things that far but again, the issue is that she is weaponizing her age to led Mimika stray. That conveys a degree of awareness that gets unsettling when is paired with the way the series has treated being a lolicon so far
Like, if I was going to say they're acting old for their age I'd probably say they're acting more like sixth graders than fourth graders but that's it really. In fact I'd probably go as far as to say Ririha acts more her age than Yuzumori?
Acting more like her age would mean she's closer to Kanna's "rival" than to Veronica trying to steal Archie from Betty.
Yuzumori actually acts like one would expect a child in her circumstances to act. Even her affection to Mimika comes off more like her seeing Mimika as an older sister or a foster mother than anything romantic.
At no point any adult has been shown in that manga. Your issues about sexualization, or whatever, are clearly not addressed in the "world" the author created and are clearly irrelevant. The author isn't writing hentai or a social comment. They are just writing a romantic comedy where some characters are 4th graders.
Stop inserting reality and your triggers in my age gap yuri manga.
You can't use this argument either because Yuzumori and Mimika's relationship isn't happening within a void ala Majyo to Houki to Kurobuchi Megane where being a lolicon was a total joke and there were no real conflict over it. Here the issue is treated more seriously and the conflict over being one is fundamental part of Mimika's character. Plus you have other characters reacting negatively at Mimika's urges. Hell, Mimika is a compelling protagonist because she is aware of her urges and does the best thing for Yuzumori regardless of them.