In my mind the distinction between the two cases is clear - the blueberry juice was a genuine accident and, FWIW I think the hotel might have viewed it as such.

I like to make a comparison between a hotel (provided it is a of a decent standard) and being a guest in a friend's home. In the Blueberry juice incident, I would expect the guest to offer to replace or clean the sheets and the host to graciously decline the offer.

In the latter case, the damage was deliberate - not, clearly an act of intention vandalism on the part of your little ones, but it wasn't an accident either. You could, and should, have seen that they had drawing equipment and weren't sat with the paper they were meant to be drawing on and, because you didn't, it was your fault.

You need to make the hotel whole and cover their losses. They, on the other hand need to not pluck a figure out of their rear end, and >$250 for sheets is insane, in a HIX even more so, so I would go back to your first reaction and write to them, offering to pay a reasonable amount to ensure they're not out of pocket but make clear that you're not going to give them a profit out of it and you're disappointed at the way they charged your card without so much as an email or letter to explain.