From a parent standpoint, they might be worried that you will collect pay in advance and not provide all the care you are supposed to???
However, if you have a good relationship I am not sure why they would think this. I would absolutely ask what the specific issue is. It may be something small and adjustable.
But it may come down to; what are you willing to do? Do you like them so much that you are going to say "This is the way it is, take it or leave it". Or are you going to make some concessions, since they have been with you for a while?