I am going to vehemently disagree with you on this arcane point. I grant you that there are indeed cases where equality and equivalence are not identical and the difference is crucial in some circumstances. But that fact is in the future for these kids, and there is no point in making them worry about this now. Just as it is okay (and necessary) to teach the incorrect laws of physics that Newton propounded (the kids' introduction to the general theory of relativity should not be in third grade, except perhaps to mention that such a thing exists, or that at very high speed or gigantic or minuscule masses things are a tad different). It is okay to tell kids that electrons go around the nucleus without bothering to explain probabilities that may be complex numbers).

Allow me to play the devil’s advocate a bit. I will note that the word mother is not equal to any of biological mother, adoptive mother, surrogate mother, nurturing mother, and so forth, but the word is indeed equivalent in most cases. But it is okay, and necessary, and socially accepted, to use the word mother for any of these. Words, in general, can apply to a range of concepts. Language won’t function otherwise. Math notation is similar: using 5*3 for what you are calling 3*5 is not abuse of notation, it is just fine.

I do unsupervised concept discovery at Pinterest (and previously at Google). Twitter: @amahabal