Some time ago I saw the beginnings of a manga, but I've forgotten its name. It's not The Promised Neverland, though there are some superficial similarities in its premise. I don't remember a ton, but there was a boy and a girl (I think his little sister, almost certain she was blind) possibly in an orphanage or school. Sorry I can't be clearer, there's a lot I've forgotten; there were probably other kids but I can't remember for sure; I think they were suspicious of the adults, but again can't be 100% sure. All I know for certain is the main characters at the start being a boy and a little blind girl.

I totally remember that one, it's one of my favorites!
I think you're thinking of Hoozuki Island/Hoozuki no Shima

Thank you very much! That's definitely the one.