Codsworth calls me mum, if you switch on subtitles you can see it

Subtitles say different.

>>#45

Well that's just silly.

It is kinda weird, you'd expect him to call male characters dad as well or female characters ma'am to fit.

Maybe that's the secret to what Codsworth thinks of you, and why you can't romance him.

He likes you as a parent.

Ah right! Didn't think of that, I was thinking in simpler terms that you're the mum of the family.