I just wanted to add that if this issue of having accidents at naptime is new, I am wondering if it is just the change or if he is drinking too much right before naptime? WHile the mom is clearly out of line for threatening you that she will leave, I do understand that she doesn't want her child to go back to pull-ups at this point especially if he will be starting school in the fall. I would make sure he doesn't drink too much before nap and make him go pee twice. Then you could ask the mom to supply waterproof cloth training pants or a waterproof pad and lots of extra clothes. This is one of the reasons that I would never have a daycare child sleep in one of my family beds. In my opinion, if I put the child there for nap, it is my responsibility to pay for damages caused by accidents. In fact, even though neither of my kids normally has accidents at night or nap, I have waterproof covers on their beds because I know that things can happen with kids. The can vomit, they can be feeling unwell and have an accident, etc.