#meanwhile he's literally just keeping charlie safe telling me to stay warm in the cold and chatting with me

[lilithofpenandbook]

This. This right here.

Charlie had been very worried about what his parents would say to him regarding his injury. Worried that they'd be upset with him for having to remain in Hogwarts because of his injury.

And the thing is, Charlie wasn't misbehaving at all when he got injured. He was careless, but not misbehaving.

So what words exactly would Snape have had to them regarding this accident?

Words that have made them so mad that mentioning that Snape (and saying he was nice to us earlier) immediately gets the two cross again, and has Molly mad at him for the rest of the event, being exceptionally mean about him (saying she isn't surprised he wouldn't have got any gifts)?

You know what I think?

I think Snape went to stand up for Charlie.

I bet he told them that their child was far too worried about disappointing them when he was injuried. I bet he called them out for putting too much pressure on their oldest children (both Bill and Charlie are worried about disappointing their parents and feel a lot of responsibility towards the youngest). I bet he went and told them to their faces that they were the problem, and not Charlie. And I bet all this because of how mad they are at him. If he'd said 'Your child is a clumsy oaf because of how you raised him', neither of them would have been this mad about it. Annoyed, yes, but they would have also told Charlie off too. But because they're so irrationally mad with him, I think what he said to them was 'Your child is under far too much pressure from you, he was more worried about you being disappointed in him than his own injury, what the hell are you doing to these kids'.

He called them out and they're mad at him for it.