There is your answer to what is happening to our country..lack of parenting skills, common sense, respect, among many other things. I would not hold back! I would ask them to replace the chalk, and the markers that were dumped into the tank, the fish and pay for the carpet to be cleaned..and anything else that was damaged...walls are probably marked up. And if they say no I would be very tempted, just to scare them, have an attorney draw up a paper saying you will take legal action $50 or so..hee hee
As far as your friend goes...I am sure she would agree. She must have a lot of patience.
You will have to let us know what they say when you confront them....I will pray for strength for you!