I’m just kind of wondering why so many people don’t say “the baby”, or “your baby” or “my baby”. We say things like “how’s baby?”.
We don’t do this for “son”, or “wife”, or “sister”. Not often, anyway.
Peace,
mangeorge
Calling an infant “Baby” rather than “the baby” sounds rather old-fashioned to me. I’ve read old books and magazines with this usage, and my mom used to buy instant mashed potato flakes that had instructions for “how to prepare [this product] for Baby” on the box. (Of course, none of us ever actually fed instant mashed potatoes to an infant.)
It’s being used as a name, with a capital B. It is old-fashioned, and you don’t hear it much anymore. At least I don’t.
I do hear people address their kids, or sometimes other children, as Brother or Sister (Sissy) sometimes, and that strikes me as a little old-fashioned too, but it is done. Especially if you’re talking to the baby: “Oh, look, Brother is giving you the car!” I know one little girl in my Sunday School class who is usually called Sissy by everyone who knows her.
I called my kids this (Baby) when they were little. It sounded (to me) more intimate, less distant than THE baby. “Baby’s up now” or “Ttime for baby’s nap.” Of course, I also called them by their names…
I like it. I will probably do the same with any grandkids that may come my way.
Fathers (or mothers) do say, “Son, I want you to cut the grass” or “you did well on that test, son.” whatever. Much more rarely, parents will say “daughter”, but that’s really old school.
I know woman in her 50s whose nickname became Sis for this very reason.
I was referred to as “The Baby” for years. I thought “The” was my first name!
Yes when talking to the person, I meant when talking about the person.
I often called my ex “wife”, but I’d never expect someone else to ask me “how’s wife?”
You’ve heard “bringing up baby”, but never “bringing up son, or daughter”. At least I haven’t.
I called my daughters “sister” when they were little. I sometimes call my grandkids “grandson/daughter” when talking to them, but if I ask their parents about them I say “how’s my grandson/daughter?”
BTW; why on earth do we call a lover “baby”?
Maybe because often lovers are engaging in behavior similar to the way we treat juveniles. Feeding each other, taking care of each other…that sort of thing.
Then when we tire of them, we refer to them as “my old lady/old man”. 
And then…horrors, THE old lady/man. Or the ball and chain.
For some reason, every time I hear someone talk to their son as in, “How are you, son?” or “Daughter, please get me my pipe,” I’m reminded of a blustering man in tails with a pocketwatch and a strong British accent. This happens even when my husband does it and just strikes me as odd. I haven’t been able to figure out why, though. It just seems awkward, like a man trying really hard to show affection to his son or daughter, but a little too stiff to unbend enough to show any real emotion. Jeez. I think I read too much.
Anyway, I often call my son baby, though generally refer to him by name if speaking about him with someone else.
I’m not sure why people refer to their kids that way - maybe because people used to have a lot more and calling one “Baby” was more likely to narrow down who you were talking about/to? And as far as “wife” or “husband,” you got me. The image I get when hearing that is more Bible belt - an old-school Baptist minister talking to his wife and vice versa. Same for sister and brother. Sort of like the minister in “Fried Green Tomatoes,” if you’ve ever seen that. Funny the preconceptions we have in our heads - before I really thought about it, I hadn’t realized that I made a distinction.
That’s a really good question, though. I’m interested to read all the responses.