Throughout most of classical and middle-ages Europe, the celebration around the winter solstice was the last hurrah before we all packed in for the winter and played the famine lottery for the next three months, especially if the lord was stingy about cracking open the grain stores. Blighted crops, long winters (pesky groundhogs), short summers (volcanic winter from an eruption on the other side of the planet! ), expansionist kings and aristocrats all would serve to decimate the population. And that's not during plague times, when an outbreak during winter could wipe out the entire village.
Children were disproportionately represented in the body count.
No amount of Jesus fixed this.
Dickens got it right pretty much with the child wretches Want and Ignorance and it is thanks to them (the tendencies in perpetuity they represent) that Christmas retains its biting undercurrent of desperation. It's also thanks to Dickens we imagine Christmas today as the family shindig. In Dickens' time industrialists really did resent their workers wanting a holiday interrupting their throughput, and people took their day off mostly to go to mass.
In fact, it was such a severe thing, I call shenanigans regarding the many-years winters in Westros, which IRL would drive our feudal societies back to migrating to escape the cold and famine. Or double down on inventing steamworks and freight.