Originally Posted by Blackcat31:
My response is always; "While normal attendance days cannot be swapped out for another, you are always welcome to ADD another day if you need it due to the holiday."
Said that way and "most" get it. 
I NEED TO START DOING THIS! same family thinks they can swap their Monday for Friday because dad wants to keep them an extra day. I’ve let it slide twice and now they are asking again. Ugh! I’m just starting this business up and didn’t realize things like this needed to spelled out in my policies.