I think 18kHz children can barely hear, I don't think they can hear above that.
The mosquito ringtones were usually lower than that.
I don't disagree with your other points, but I suspect that frequency range won't be detected.
Lighting occupancy sensors are the worst.
And yes, I've had my hearing tested, and I am in fact, a freak.
It's rather common to assume that a good share of the adult population is near deaf.
A few years ago I went to a restaurant with outside sitting near Big Sur. There was a nearly unbearable high pitch whine of which most other guests seemed blissfully unaware. I asked a waiter about it and he informed me, that they recently installed a system to shoo away birds from the tables. I think they also shooed away quite a few customers.
I don't think it's outrageous to claim that this is the comfortable range for most adults who experience some kind of hearing loss over time with age.
Children most definitely can hear above 20khz. I at least have the anecdotal experience ("most" here is keyword to argue against) that I experimented with testing ultrasonic frequencies on multiple devices to see if audio file formats made any discernible difference in range performance. This involved "swooping" a frequency starting at 20hz to as high as you can emit it (which usually starts to sputter in consistency around 18kHz.