If they did come back and ask for a space I certainly would bring up my reservations concerning the germs. Use the idea that children not exposed to a certain amount of "dirt" do not develop a good immune system and are constantly getting sick which will be a hardship for both baby and parents. Even if they then get upset with you say at least you will have done the child a service by planting the bug to lighten up on the sanitizing.
I have also found though depending on the age the child is at the interview that what parents do when child is 6 months is different than when they start at a year in the sense that once the child is down on the floor and moving around they realize what we already know and that it is a hopeless cause and at least one person close to them also probably tells them. By the time the child starts care they expect clean but not to the degree at the interview. So there may be hope but it does have to be discussed as an issue and not just assumed.