This thread is batshit. I don't see how anyone can think you're unreasonable @putmeonthebackburner And I am a mum of 2 DC. (Had them in my late 20s.) Of course parents want time off at Christmas with their children, but to suggest child free people should be treated as lesser (and not as deserving of Christmas time off!) is outrageous.
And wtf are grandparents in there for? (On your workplace list!) Why do THEY need time off? 
Reminds me of a bloody woman who used to work at my DH's place. She was part time (3 days a week,) and has a daughter in her mid 30s, and she looked after her daughter's little boy for around 16-18 hours a week, whilst the daughter went to work, or went out to play badminton, go swimming, go to a hobby group, or when she went shopping etc...
This woman worked Monday, Wednesday, and Thursday at the place that is open 7 days a week. (6 to 7 hours a day) A new manager started, and told her she had to do her share of weekends, and she went batshit, refusing to do it, because she looks after her grandson every Saturday!
She couldn't understand that no-one gives a shite about her 'grandparent duties!' He wasn't HER son, he was her daughter's son. She also had a son herself who was about 7 years younger than her daughter, so she had already had mummy privileges for some years, now she wanted them as a grandmother.
tl;dr, the manager dug his heels in and she ended up leaving.