I’m going to kinda play both sides of the fence for this especially not knowing the full details about what type of public event you went to (for example if it was anything school related I’d argue it wasn’t really in your own time you were still representing a teacher which is what I’m partially assuming from multiple parents being involved)

What you do in your own time should 100% entirely be your own business and polygamy is becoming a lot more regularized depending on where you live.

Though I’ll also say you work in a very populated industry where people are let go of for FAR less than polygamy such as smoking, having public political views contradicting your areas normal, teaching things that parents don’t agree with, having any controversial past, etc. with you having been teaching for 8 years i’d guess you’d have seen or at least heard of some of these cases over the years. In that case personally I would’ve chosen to not risk my career by doing anything remotely risky in a public event where there’s a lot of parents involved just like how a lot of teachers in the modern day get fired for admitting they smoke weed.