It’s not an ad hominem. It’s a polite way to suggest that you don’t know what you are talking about when it comes to teaching concepts to kids. I think it’s worth your while to wonder why it is so obvious that you are not a teacher. What experience and insights regarding age appropriate explanations are you missing that make it so obvious that you don’t teach?
Correctness, of the sort you are implying are absolutely not appropriate at all levels. There’s a reason kids in second grade are told that you can’t subtract a larger number from a smaller one, for instance.
1. None of what you are saying removes the ad hominem aspect.
2. In grades 1-2 (iirc) we applied negative numbers when we talked about the number line (which we had on the wall.) Even preschoolers knew about negative temperatures on the thermometer.
You don't need to tell kids things that are misleading nonsense. It only confuses them more. You can be precise and high level at the same time.
In no sense do computers struggle with digits. That's a misleading confusing statement and it's not appropriate at any age.