For what it's worth, (and I am not a lawyer so this is just a WAG), I'd bet that it won't invalidate the tens of thousands of same-sex marriages that have already been performed, or will be shortly in the scramble before the vote is certified, and the amendment is officially enacted. For better or for worse, those marriages were/will have been legal at the time they were performed. And ex post facto laws normally don't cut it.
FWIW, I am the father of a kindergartner, and I am not at all concerned about the extremely remote possibility of him being taught about same-sex marriage in school. I am, however, concerned that they're already teaching him abstract graphs and Venn diagrams.
I don't recall much of my own kindergarten days, but I'm pretty sure we didn't go much further than petting bunnies and making applesauce.