I have it listed on my website (several times) that I have a cat. I have only had one family cancel because of my cat. I also put it on most of my adds and have a sign on the outside and inside of my cat asking : "Please don't let the cat out."
I also have it in my contract:
"Animals in the daycare
There is a cat in the home Daycare at all times. I ask that you please don't let him out and respect the fact this is his home. He is vaccinated yearly. Please also keep in mine that although my cat is friendly he is still an animal and has the right to defend himself if he feels threaten."

I also make sure I mention the fact I have a cat in the interview. I have had 2 family's tell me that they are allergic during the interview.