In the case at work, it is just a general bright happiness, like a girl speaking to her father, no baby talk.
One of my cousins has always had a “little girl voice.” TBH I haven’t seen her much as an adult (she is a wife, a mom of 2, and also a nurse) but when I see her she still has that voice. I think she has body dysmorphia. She has always been someone I would consider a “hot blonde”, yet she has had both breast implants and butt implants to change what most would consider an already better-than-average body.
If you listen closely I think she speaks with a very nasal voice, and always has. I assume she started doing this on purpose to make her voice sound higher and it became her way of speaking.
Here’s a very awkward example, @Kimstu, of a young transwoman who is very clearly trying their best to speak in a “little girl” voice as their normal voice. I can’t imagine trying to transition as your body is desperately trying to take your voice the opposite way. You can tell she is putting a lot of effort into it. Her main tactic seems to be “the quieter the better” so at some points in the show she can barely be heard, especially when she’s emotional.
I know trans people and especially trans teens aren’t part of this discussion - we’re talking about adult cis women who speak in a way that makes them sound like little girls. But I wanted to use this clip as an example of a person who is trying to speak like a little girl and their interpretation of what that voice is. Plus I just binged this show this weekend so it’s fresh on my mind.
I promise I’m not being obtuse on purpose here (can’t do much about any inadvertent natural obtuseness that may be affecting my reactions, sorry), but I still don’t understand the association between an affect of “general bright happiness” and the impression of “a girl speaking to her father”.
For example, my own typical affect in work conversations would probably be described as something like “general bright happiness” (yes! the surly combative Kimstu of the SDMB is not the only existing Kimstu! 
), yet I don’t think anybody’s ever got the impression that I sound in any way “childlike” or “like a girl speaking to her father”. Is it just because my voice is low-pitched, or I often use big words, or what?
Or is it mainly, as I’ve noticed before, that there is a socially baked-in predisposition to associate women with “childishness”, and behavior patterns that wouldn’t seem “childlike” in men come across as immature or juvenile in women? A low voice or a more sophisticated verbal style may be counterbalancing that predisposition in my own case.
I’ve known two different women in my life (one was a girlfriend other was a sister) who had two distinct voices. They had a really high pitched “happy” voice when they were meeting new people or talking in public, and then a much lower more “normal” sounding voice when talking with people they already knew or were in private. They both SWORE they never changed their voices even when you recorded them and showed them both variations, so I don’t know if it was sub-conscious or if they were deep in denial.
Paris Hilton and her mother famously have an affected baby voice. Search YouTube at your peril.
Now she doesn’t sound to me like she’s doing the “little girl” voice at all. I’d say she’s passing better than a lot of the voices I hear. Breathiness can hide a lot of the timbre of the voice. I’ve definitely heard a lot of cisgender women who sound like her.
It doesn’t sound at all to me like the typical affected baby or girly voice. It sounds more like she’s been involved in feminization vocal training.
It’s actually difficult to learn how to keep your voice that light without being breathy. It takes a lot of breath support.
And then, there’s this:
Could there be sexism here? I mean, have you ever heard Ira Glass? He is a phenomenal journalist but sounds like a voice-cracky 14-year-old boy.
I thought it was adenoids.
His voice is strange, but I wouldn’t describe it as childish.
More like a really dumb guy with adenoids.
I think there could, especially in the assumption that a woman who has “a high, light voice” must either be assuming it as an “affected” mannerism or else be suffering from “some sort of speech defect”.
Again, it’s part of our societal programming to believe that men can have a wide range of individual behavior variation that counts as “normal” or “acceptable”, whereas the range for women is much narrower. An NPR segment entitled "Talking While Female (apropos in light of the context of the OP) starts off with some of the unsolicited criticism received by female NPR announcers on their voices:
I mean, I believe that people who complain about the sounds of women’s voices are sincerely bothered by what they hear, they’re not just maliciously making it up to be insulting. But I think that most of us don’t realize the degree of cultural brainwashing that has produced our default mindset of being hypercritical of women’s voices.
Funny how when it’s a man, it’s a matter of physical issues, but with a woman, it’s an affectation.
Certainly actresses will affect a high pitch for an acting role (like the woman on Will & Grace), but all the women I’ve ever known with high-pitched little-girl voices simply had naturally high-pitched voices. And, yes, some people speak in a higher register when they tense up or get nervous - men as well as women.
Sounds like you’re simply describing her physical anatomy.
Does not follow (bolding mine).
Here are three textbook examples:
Actress Joey Lauren Adams (Clerks, Chasing Amy) speaking with Conan O’Brien in 1997.
Acress Jennifer Tilly (Bullets Over Broadway, Child’s Play) speaking with Conan O’Brien in 1994.
Actress Zelda Rubinstein (the medium Tangina in Poltergeist, the organist in Sixteen Candles) speaking with CNN’s Bill Tush on People Now sometime in the mid-1980s.
FWIW, Rubinstein is 4’3" in height. Adams and Tilly are 5’6" and 5’7" respectively.
Someone mentioned Blossom Dearie upthread. I’m familiar with her singing from Schoolhouse Rock, but had never heard her speaking voice. In the clip below, she begins speaking shortly after the 1:00 mark.
Wait, that sounds like a “high, light” or “childlike” voice to you?
“It’s about a guy who falls in love with a lesbian, finds out she’s had heterosexual relationships and can’t deal with that […] It’s a really honest film […] I’m really proud of it” […] “when I came on, which was about 45 minutes into the film, that I was Andie McDowell in a black wig” […] “I go into Home Depot a lot” […] “I honestly love that place”.
Absolutely none of that sounded “little girl” to me, and I typed out bits of it to see if there was some especially childish syntax I wasn’t noticing.
Adams’ voice sounds youthful and casual, and she’s very smiley/laughy/bubbly especially at the beginning (which seems to be kind of de rigueur for young beautiful actresses on talk shows), but to me it would be a pretty big leap from there to actually “childlike” or “like a girl talking to her father”.
Equally mystified.
“I think you should give me and your studio audience special kudos for showing up the day after Christmas” […] “Did you really see the Woody Allen movie?” […] “I assume this is my water, thank you” […] “I was hoping that throughout the show you could sprinkle the phrase ‘Oscar talk’” […]
Her voice isn’t even particularly high or light, much less “little girl”. Again, it sounds youthful and friendly, but I am not getting the perceived overlap of that with “childlike”.
Rubinstein definitely does have what I would consider an unusually “high” and “soft” voice, which AIUI is in fact not unusual for little people. And if she were saying dialogue like “Mommy can I pweeze have ice cweam”, I could easily believe that it was a little girl speaking.
But after a few sentences like
“I wouldn’t have accepted that role under any circumstances” […] “I’m not fearful about phenomena I don’t understand” […],
I just don’t get the “little girl” illusion from her sound anymore.
That sounds “little girl” to you?? It’s definitely on the light and breathy side, but her diction and very precise articulation sound to me very mature and sophisticated. More so than Adams or Tilly, who have more casual speaking styles.
Here’s a question in return: Do you think that in those linked interviews, Conan O’Brien sounds more “boyish” or “light” than Bill Tush does? Does O’Brien’s voice come across as kind of “little boy” to you?
Syntax and subject matter aren’t relevant to the matter, IMHO. So far as I’m aware, it’s generally a matter of anatomy.
Please note that I’m not making a value judgment or expressing contempt regarding these women’s voices — I’m just noting an impression.
…
Regarding Dearie, I had not heard her speak before seeing that clip. She generally does not sound child-like — but I have an unsupported suspicion that she works at her presentation a bit, as Kathy Ireland has done. In a few unguarded moments, Dearie sounds a lot more youthful for a phrase here and there.
Syntax and subject matter aren’t relevant to pure physics questions of sound frequency, resonance, timbre, and so forth, sure.
But they most definitely are relevant to observers’ subjective impressions of what a voice “sounds like”.
Yes, that’s perfectly valid. My point is just that I suspect your impression is somewhat affected by societal conditioning, rather than being a pure unmediated response to differences in auditory stimuli.
And again, part of our societal conditioning about women is that they have a much narrower range of admissible individual variation, without seeming “annoying” or “distracting” or “weird” or “unserious” or “babyish” or “repulsive” etc. etc., than men do.
You hear that O’Brien’s voice is higher and less polished-sounding than Tush’s, say, and you just think that that’s O’Brien’s voice. Your brain doesn’t lock in on the impression that he sounds “teenagerish” or “juvenile” or anything like that.
But you hear that Tilly’s voice is different from, I don’t know, Katherine Hepburn’s? in a similar sort of way, and your conditioning starts telling you “little girl” and “childish” or “silly” or “airhead” or whatever, and that becomes the defining aspect of the sound. It doesn’t get processed as “that’s just her individual voice” the way that a man’s individual voice typically does.
I don’t believe Glass has a child like voice, it is vaguely adenoidal, and flat, with no intonation. Perhaps he thinks a radio voice should be different than a speaking voice.
Not childlike but adolescent. I have no idea what folks mean by “adenoidal”.