One reason I love this arc - and especially the scene with the social worker interviews the Batfamily - is that it acknowledges that the relationship between Bruce and the Robins can look iffy. Bruce took in both Dick and Jason as older kids (Dick even got aged up to twelve, and Jason was supposed to be twelve or thirteen), and Tim lived at Wayne Manor when he was around that age too. Teens and older kids almost never get adopted because people want young kids; Bruce's interest in becoming Dick's guardian could be easily explained in the similarity between their histories and the fact that Bruce was there when Dick's parents died, but with Jason and Tim it's a pattern. Rich bachelor billionaire living alone with his butler regularly takes in kids, the oldest of which abruptly left home at nineteen and was replaced by a younger model with a shady history. There's no way this wouldn't look suspicious in our world.
Cass' case is only slightly different - read: better - because while she looks very young as well and probably underage, she doesn't legally exist. There are no papers, no family name linking her to Bruce Wayne. It's important here that she's not his daughter in the eyes of the law; the social worker's investigation only concerns her because she cares, not because she's in the middle of it. She's a girl and she's there and she may or may not be one of Bruce Wayne's conquests and that makes her out of reach for the investigation.
Incidentally I read Cass' remarks to the social worker and to the boys as humor and curiosity, because otherwise I'd have to admit that it's some horribly written Cass up there - the characterization where she speaks little because she's too wise for words rather than because she doesn't get words - so I'm choosing to read it as Cass attempting to communicate with the others in the way both Dick and Tim do, with words and puns and humor.
I'm glad Tim's the one to react directly to these implications as well; he's always been the "meta" Robin, he's always been written as the one most aware of the roles and masks, so it's fair that he gets to remark on things people out of universe comment upon.
"I allowed him to have hope and it killed him" remains one of my key sentences to explain Bruce. And it's so ironic that the social worker's name is Felix Desidero. (Beatty must've been so proud.)