It's not easy when rules that feel targeted at you are implemented. I empathize with the mom in this story because her kids' exclusion feels a bit like high school. She is the only person in the family with young children, and her sister decided to implement a "no kids" rule for gatherings at her house. That wouldn't feel as rotten if most of her siblings had kids, but then again, it might not be as enforceable if other family members didn't tolerate their exclusion.
That being said, there's a big difference between children being excluded from one person's house and everyone's house for all holidays and events. The mom in this story assumes that because her sister doesn't want her kids in her house (and all other family members agree on those terms), they're going to have child-free family Christmases hereafter, which is a silly conclusion to jump to.
This image is for illustration only, and the subjects are models; the image does not depict the actual subjects of the story.