Thanks all for the replies! I thoroughly enjoyed reading all of them. I thought it was an odd thing for HC to say so that's why I asked. Wondering if this was a common things in other gyms or the workplace in general. I'm happy I asked as a lot of you brought up some great points.
While HC made it out to be a "volunteer" type event, it is definitely expected that we are there and it would look pretty bad if none of us showed up. And we will still be doing work related activities as I explained previously. This is not a parent-run event. Parents just drop their kids off and pick them up in the morning, except for the few parents that are coming in late and staying overnight with HC.
I bought this up to the other hourly team coach, to see if she had any issue with it. She was completely on the same page with me, but didn't want to speak up as she thought it was a standard practice. We will for sure bring this up in our meeting this week, and if all fails, bring it up to the business manager.
Our hours are already going to be short this holiday season as our gym is taking several days off for Christmas and then several more days off for the New Year...so we are already losing $. Not that we're in this job for the money, lol. But ya know, we have presents to buy, too. And taking out a whole other day of practice that we won't get paid for doesn't feel right to me.