I, too, would PASS on any parents who are going to call into question your policies. A question out of curiosity is one thing, but to tell you that you can't put your own guidelines into place....????
These will be the same parents who ask you to change your menu, hours and rates to suit their personal preferences. No thank you.
I think you need to ensure that what you practice in the way of policy makes sense for you, your business and your family. You want to make sure that it is reasonable in regards to the "norm" for your area, but even at that it is YOUR business. If a prospective parent takes issue.... they can find another provider.