I can tend to be passive-agressive, but when something like this comes up, I'll say things like "Oh no! What are you going to do? Can your mom come and stay with you? Can you use sick days? Oh my, I hope your boss isn't too upset! Too bad you've already used up your personal days!"
But yes, I know, that's just evil
Don't even give that family a second thought. Don't worry about how they're going to find care for THEIR child, and enjoy your vacation!!