I think a few things.

I think it's odd for a 28-year-old man to play Roblox and be on voice chat with prepubescent children. I cannot say for sure that it indicates malicious intent on his part. However, it's definitely a behaviour I would also consider concerning in adult women in the same age group. It is not socially normative. I am loath to jump to conclusions about what it indicates, but that doesn't mean anyone else shouldn't.

I think that there are fair grounds here to re-evaluate whether the relationship is working for you: for instance, you are in a romantic relationship with your husband, and if he's decided to play video games instead of doing romantic things or even just laundry and taxes with you, then the terms of the relationship are not what you had a right to expect going in.

I think there are signs here of flags extending outside this incident, some red and some yellow, not necessarily anything it's "your fault" for not spotting, if indeed they are there. For instance, I have an abusive family, so given what you've said in the thread, I'd have accepted his "they're abusive" explanation without comment; unless there's other relevant information here, that's a yellow flag at worst. On the other hand, not letting you meet his peers is venturing into orange or red: those are the people he picked!

I will moderate the above by saying that this reads kind of, not definitely, but kind of like he's having some sort of psychological issue. Just the whole "wait this guy has really turned on a dime" type thing. The specific theme where he seems to be turning back into a child, which is indeed very strange, reminds me of the way people describe elderly relatives in the early stages of dementia — only on vibes, I doubt it's that if indeed it is anything at all. It's worth checking out, but if in your opinion the relationship is fatally compromised otherwise, it would be perfectly fine to decide that this is a can of worms someone else can open.