Then in that case it’s the manager’s job to sort the issue, isn’t it? If someone can’t work due to lack of childcare then they can’t work, as they can’t leave their children home alone. If there is no one willing or able cover that shift, then it’s an issue for management to sort.
This. I've been a single mother who suddenly needed to sort out childcare where once my children's father was automatically around to do it. Guess what? He was still responsible and, as he worked in academia, was off for Christmas whilst I wasn't always so in the years I had to work we worked it out together to ensure those were the years he had the children over Christmas. It's shit, but hey, our kids, our problem.
I've also been the manager who had to tell parents complaining about working that they had to suck it up and have their husband, partner, parents, other regular childcare that I knew they had access to.
The single parent with no support at all is rarer than MN would have you believe and, if that is your life, then a career in a field where there is a need for Christmas working might not be for you at this time.