"And of course, you are always adding to vocabulary and increasing the complexity of sentences as your child develops. Children are learning thousands of words per year from 0-4/5/6 through constant exposure/repetition. Though they are very abstract concepts, the words themselves may have a meaning for them (depends very much on the individual child and their experiences and associations) although a negative association is more likely than an understanding of meaning (adult seemed agitated, adult raised voice, adult swept child away from item that was dangerous or took item away fast) the actual danger (electrocution, blindness) that bothers the adult may not be understandable to the child. The effectiveness of teaching the concept of 'dangerous' to children of 4 needs to be viewed in the context of their tendency to be magical thinkers, to have a difficult time with the concept of permanent change like death or blindness or disfiguration or burning the house down they have no prior experience against which to measure the concept of a disastrous outcome to something 'dangerous' they do. Wishing dead relatives or pets back is characteristic of children of age 4 when dealing with death or disaster. Many develop superhero fantasies where they are the stars."
Sigh. Yes, of course. None of this changes the fact that you said it was impossible for a child of 3 and a half to understand the word dangerous.
Yet again, thanks for teaching me all of this. I didn't know any of it before
even though it is my job to explain this stuff
You're kind of shooting yourself in the foot here, math too. The negative association is the first feeling/meaning attributed to the word dangerous, a sort of prefoundation of semantic meaning if you will. Unfortunately if you take that logic (and don't believe that there is what we might call a "relational frame" developing whereby the word danger/dangerous extends to other elements of the environment in a way mediated by language), then you are actually supporting a position where it would make sense to smack a child to stop them from doing something dangerous e.g. the smack would signal danger/act as an aversive reinforcer or punishment which would be likely to reduce the recurrence of the behaviour in the future.
Adults negotiate the development of meaning through their actions and the language they use. This is part of the reason that it differs from child to child depending on their associations. Experiences and how adults react to and explain them to children create meaning in conjunction with the child's focus at that point in time.
"If it was truly dangerous and very important to stop immediately then attempting to use the occasion to expand vocab would not be a sensible option for the adult."
As for this, ffs. Really!!! Thank God you have informed me of this, there is a lightbulb flashing over my head because I was saying the opposite to this in challenging one sentence of yours, which is that a 3.8 year old couldn't possibly understand the meaning of the words danger/dangerous
The point is that whatever you do children will be making associations. If the word "danger" and "dangerous" are used in any way whether consciously on the part of the adult or not, the child will "bank" this as part of their understanding of this word. That is part of word learning. If you smack while saying "dangerous" and it creates a negative association, that will become part of the meaning of the word. I don't advocate that, but it is a basic tenet of both behavioural and neurodevelopmental accounts of child language learning.
However, feel free to continue expounding on why I am wrong here...