I had a family that did the same I charge an extra fee of $7 a day. I explained when the kids are napping I get some paper work done have my lunch and get things ready for the afternoon. If they don’t want to follow my rules and take that time from me then I will charge a fee for the 2hrs for all the work I won’t be getting done seeing that this child will now have special needs. The mom said that was fine but after a month I found they didn’t want to pay the extra, so we get him napping once a day. Good luck