Well it looks like nobody else is offering any alternatives outside of the comments yet, so while I am hesitant to make the following suggestion as a means of describing a child, it is surely better than any phrase using the word "bitchy". It is more of a relative compromise between politeness and accurately describing the phonomena, than an ideal example of either. It is less sexist at the least.
One way to describe an uncontrolled expression expression is “natural”, rather than resting, particularly with this definition of the word:
- Not forced; not far fetched; such as is dictated by nature.
The gestures of the orator are natural.” — The American Dictionary of the English Language (A.D.E.L) by Noah Webster
You would apply this adjective to the expression itself. We often enough call smiles natural that the 2013 Kernerman Multilingual Dictionary exemplifies “a nice, natural smile” under the natural entry. Another expression we sometimes, albeit much more rarely, describe as natural is the scowl and I suppose this pop culture phenomena is following that example, except in a more jocular manner:
“Verb 1. To wrinkle the brows, as in frowning or displeasure; to put on a frowning look; to look sour, sullen, severe or angry.
She scowl'd and frown'd with froward countenance.
Noun 1. The wrinkling of the brows in frowning; the expression of displeasure, sullenness or discontent in the countenance.” — A.D.E.L.
It should be noted that this word combination, has an equivocal signification by way of unknown reason. Perhaps the reason you have a natural scowl is because you are an inherently morose person, or perhaps it is the most natural face to have under the given circumstance. Nevertheless, it seems to have been used to describe an innate scowl as well.
"Comedian Taylor Orci says she was one of those people who has always had a natural scowl, even when happy, and that strangers have come up to her to ask her what is wrong and tell her to smile. So she created and starred in a humorous short video on bitchy resting face that has gotten more than three and a half million views on YouTube and brought BRF to widespread public attention." — ‘Bitchy Resting Face': What That Grumpy Look Really Means by Laurie Sue Brockway, Everyday Health Staff Writer on August 26th 2013
Lest anybody thinks otherwise, I will say I was not actually looking for information regarding the phrase natural bitchy face when I found this quote. It is actually my top result on Google for a natural scowl search. It is even the excerpt Google chose to exemplify for some reason. This is already looking like a good match.
In search of a more direct quote, I also found N.B.C. Today Mind Your Mannerisms segment where Taylor Orci is interviewed by Samantha Gurthie. When asked what her inspiration was, she responded “When my boyfriend and I met, uhm, he thought that I had a scowl and I was like, uh, oh God, he doesn’t look so great himself.” Although I can’t date the interview itself, a video of the interview can be presently found attached to the July 2nd 2013 article “TODAY anchors check if they have 'bitchy resting face’ by Scott Stump which also summarizes it.
N.B.C. Today also interviewed the Michigan based Plastic Surgeon Doctor Anthony Youn to ascribe the cause of this look. Doctor Youn primarily attributed the phenomena to the tendency for the lips to droop into a natural frown, with deep vertical lines near the eyebrows. C.N.N’s. Jareen Imam reports in ’Resting Bitchy Face’ is Real, Scientists Say, that Abbe Macbeth and Jason Rogers from Noldus Information Technolgy picked neutral looking faces and ran it through their “objective” facial recognition software to determine that 3% of them registered as sad, happy or angry. Most of them were registered as expressing contempt, which is interesting because Macbeth mentioned that slightly pulled back lips and squinting eyes were read that way. Those sound like the objectively recognizable qualities of a scowl to me.
Because I lack a dictionary definition for a relatively literal word combination, I feel as if it is imperative to show some form of prior usage, particularly in the applicable sense of the words. These are a few of the quotations which I think best exemplify use of the words in this manner:
“And she was really quite good in her way, you know — with a truly horrifying natural scowl. Her legs were never photogenique but we kept her in long skirts and used an understudy for the lower half in scenes of violence.” — Horizon, Volume 17, Issues 97-101, page 80, 1948
“The first comer was a tall, fair youth, with a soft face, pink and white as a girl’s —a pretty face with tip tilted nose and an indescribable impression of airy impudence. Behind him came a thick-set man the natural scowl on whose countenance was now intensified by some inner heat of anger. He did not speak, but stared angrily at his host from behind Mr. Martindale’s slim figure” — The Cornhill Magazine, New Series published by London Smith, Elder, & Co., 15 Waterloo Place, Vol. XXIII, July to December 1907
“He is ruggedly handsome, which is another way of saying that brute strength and athletic prowess can change public perceptions of beauty. He wears a natural scowl, even when he is perfectly relaxed … He might as well have bolts sticking out of his neck. Other than that, he’s a regular guy.” — Cold Cocked on Hockey, by Lorma Jackson, page 96, 2007
Around the internet it seems that people are using these words self descriptively do ascribe the exact condition. You can see one such instance in my demonstrated Google Search Results from before, since I could not make the window any smaller for the screenshot.