Is it after work or during work time? You just say, sorry I can’t swap days and that’s that… If it’s after work it doesn’t matter what day it is, you’d need childcare, but if you don’t want to go that’s ok, but nice to be asked & feel included too
Just say you can't get childcare and that's it.
They def can't make you go to a social...
Surely the Christmas meal is optional? If you don’t want to/can’t go then just tell them. I rarely go to things like this at my work as they are often in the evenings so childcare would be an issue and also are expensive. I’d rather spend my time and money on other things 😂