That will eventually happen anyways. Isekai genre wont care about the mental age of mc
Idk why but this manhwa feel different like these children are acting their age whereas something like I'll be the matriarch in this life both the fl and ml were not acting their age and the fl treated him like a kid
Probably because the FL never gets to grow past the age of 18 or 20 and this is the first time she actually has a non-traumatic childhood. So she never truly got to be a proper kid and she’s in no hurry to grow because all that means to her, is she’ll die.
Like in most isekais the people who actually die are usually in their early 20s and also they dont completely remember their past life once they prohress their next life as a baby so that can be one factor why the mental age is somewhat same as their physical age in the current birth.
For the mc in this story, well other than the awarenesses maturity around her is more but again she used to die everytime after she turned 20s so theres her mental age reset too.
Please don't make her fall in love with the blonde kid. it's not like she is even mentally a child she is more like an adult even when it comes to her way of thinking