It also hasn't been established whether the hotel made any attempt to clean the sheets -- apparently not if the timing of the charge is any indication.
^
OP should check the brand of his kids' markers. Here's part of an
Amazon review for one Crayola set:
my 3 year old twins got hold of these markers, and while we thought they were taking a nap, they decided to color my (expensive)linen! When I saw the extent of their decorations, I honestly thought that it would not come out, sheets, bed-spreads, pillow cases, the works. For whatever reason, I was not able to wash the linen for THREE days. I soaked each set separately in oxy, then ran it through the washing machine..... and PRAYED!
When I took out the linen from the wash and inspected, I turned it back and forth over and over - I was shocked. There was NOT ONE stain on the linen!