Then what's the point of them being reincarnated with the memories of their past lives? they think and behave like any abused 5 yo child would. I think these stories would be cute without the reincarnation, it seem like the author just throw the reincarnation into the mix for the sake 'oh it's popular theme nowadays' kinda thing,
Yeah I make that point a lot too in some of these kid stories where ppl are like they're not acting mature even though mentally they're over 20 something blah blah blah
Like you said, they died at 18 so even though they've lived another 5 years after being reincarnated that doesn't give them the knowledge of being over 20. No, the most maturity they know is that of highschool in their previous life and then they had to start over in a new world all together and were abused and all that stuff upon starting over from children.
So overall the most mature they can possibly act is that of a teenager, they never reached the age of 20+ so how can they act mature like a 20+ year old.
And with that said that's really the only reason I'm not completely bothered by ariens little crushes, I mean it is still not appropriate for her to be having love interests at the age of 5 but at the same time with the mentality to a teenage girl it's totally plausible for her to be having crushes on good looking boys and such. Although to everyone else in the world who view them as 5 year olds it's totally weird to view them in any sort of romance situations until they're much older (〜 ̄△ ̄)〜
these two were 18 when they died, technically with their added age they'd be 26/27 (I forgot how much time has passed) but considering they said they were high schoolers, with no mention of gradation, their adult knowledge is limited
they don't have the experience other 26/27 year olds have since they died and started over, all they have is what they learned in their previous lives, which isn't helpful in this fantasy setting, and trauma