I don't believe the International Astronomical Union has offered an opinion about the Webster's definition of the word, or about how you and your six year-old may use "planet" in ordinary language.
The IAU's definition is a scientific definition, one that pertains to usage among astronomers. Insisting that astronomers make up another word is silly for all the same reasons that (as you pointed out) it would be silly for astronomers to tell us how to use one of our everyday, non-technical words. The same sequence of characters or phonemes can have slightly different meanings in different contexts.
But the IAU definition makes no sense for astronomical use, particularly as we get better at finding extrasolar plane^H^Horbital bodies. We're going to have hundreds of repeats of Ceres/Vesta/Pluto - bodies that we discover, consider to be planets, and then only much later with finer techniques discover that there were other bodies in the same orbit. That's not good for science.
Upvoted, as this is an excellent point. The IAU definition makes serious presumptions about our level of knowledge. Could the IAU definition be used at the time of Pluto's discovery? If not, what does that say about using this definition for future discoveries?
Note that I'm not saying that I think that dwarf planets should be categorized as planets (there are too many), but that the definition shouldn't depend upon us having complete knowledge of every object in a newly discovered potential planet's neighborhood.
The IAU's definition is a scientific definition, one that pertains to usage among astronomers. Insisting that astronomers make up another word is silly for all the same reasons that (as you pointed out) it would be silly for astronomers to tell us how to use one of our everyday, non-technical words. The same sequence of characters or phonemes can have slightly different meanings in different contexts.