the infantilization of Roxas is one of the worst things about Days imo.
That's also my opinion and why I'm also sharing Blackdrazon's point of view on the game so far.
I also get your perspective Hirokey, how you see Roxas' character, but I don't think these justifications make any sense in explaining Roxas's actions. Roxas doesn't behave like a toddler, he never does, so that he's only one year old doesn't make any sense in this regard.
He lacks perspective, enormously so, because he doesn't have memories and therefore no experience and is manipulated on top. He's more like a robot that gets self-conscious but he is
able to think and act more complex, something a toddler simply can't, and we see that in the games too. He can be rational, he can even read, and write and probably calculate, but he doesn't seem to use these skills in some cases.
This incongruity between the actions of Roxas, his perceived learning and what the story tries to hammer in, is where the game truly fails for me. It fails even double because it's the same for Xion too and it fails even more because this very same story worked so much better in Naminé's case.
I totally get when the story of for example BBS is criticized for being a rush-job when the friendship of the three main characters is never really explained or shown for example, but at least in this case you can fill in the gaps very easily. In Days' case the whole premise is borked from the start, and never worked for me and what's even worse it made some of the good scenes in KHII questionable or downright strange (like the meeting with Xemnas on the Dark Margin).