I can only tell you what I've heard:
- Some places have policies for their own reasons that demand blood pressures on all patients, including all peds.
- Because of ^ this, some nurses put blood pressure cuffs on every peds patient, whether squirming, clenching, flailing or screaming bloody murder, and will enter the resulting value into the chart.
- Some nurses assess patients by other means, including those you have mentioned, and make an attempt at blood pressure; if it is clear that an accurate value cannot be obtained in a low-acuity patient at that time, the attempt is abandoned.
There's no arguing that in general children should be screened and monitored for hypertension. I haven't yet read any widespread standards about how a blood pressure on a frightened, crying/screaming, active or resistant patient has anything to do with appropriate screening.
The referenced article was interesting, but due to innumerable observations, I don't think that their definition of calm is sufficient and I also doubt the accuracy of the determination that a child was calm.
My experience is that it's fairly rare for a generally healthy infant/young child at a lower-acuity ED visit to tolerate a blood pressure without the fine movements they usually do in response to it: the fine clenching, twisting and intermittent muscle movements--even when they otherwise could generally be said to be calm (even cooperative).
There are other factors (anecdotally) that would also suggest that a triage b/p is particularly worthless even if a b/p was absolutely mandatory sometime during the visit. They come into the triage area and, whether in pain or particularly fearful or not, they are encountering stranger, they're very curious about their surroundings, they are uncertain about what's going to happen to them or if it's going to be painful or scary.
I would make the argument that in the absence of conditions (whether congenital, chronic/acute, etc) that place them at high risk, this is a very low-value activity in the ED.