Don't have any pets now. But I don't advertise or say I'm pet free. When I first started we had a collie / lab mix and parents did not mind. He sadly did pass away a few years ago so now we don't have them. But out of my daycare kids all 3 have a least one cat. And the child who has a vet as a parent has dogs as well. I'm hopping to convince my husband to get a cat soon.

They may be some who choose to go with a pet free home so you would loss out in those familys. Since you do advertise as such would be required to give notice to parents in case it will make a difference to them (be prepared to loss a kid if this is the case). Also you would want a place to keep kids and dog seperated expessilly while training the dog. But I see no over all problem of adding a family member to your house.