Lab rats. If they weren't on the streets before, or wherever you grab these people from, it's like..
Ok, so, imagine you took an already existing child or just created a new one by growing it in a lab tube or something.
If you don't give them a parent-like figure, someone to actually teach them stuff, when if they grow up as adults they won't match the typical schema of an adult.
And I'm not even talking about the 'general knowledge'. Whumpee that's kept in a lab all their life won't know what taxes are. Or shops, or cars, or math, whatever. We expect that.
We expect adults to know about privacy. Whumpee doesn't have problems with removing their clothes. That's just a body, right? They usually walk in paper like hospital gowns anyway. (No, wait, this one actually is not a breakthrough, we expect that too)
We expect adults to know how to keep themselves alive. Whumpee might not even know they need to eat if their whole life they were hooked up to a feeding tube.
We expect adults to know how to communicate with people. Whumpee probably knows one language. The one scientists use. It'll lack common words. It'll be full of specialist lab words. Not ideal to use in a conversation. Whumpee might use more sounds. Whines, snarls, screams. That's the easiest way to communicate they're in pain or angry or scared.
And there's probably a lot more stuff like this.
That doesn't mean they're stupid. Hell, make them very intelligent. I'd love that. But because of the environment they've grown up in, their behaviour will be different from the regular people.
And now take them out of that lab, throw them into Caretaker's house and let them figure it out.