Oh wow, that would freak me out too.

I don't advertise unless I'm actively looking and I try to not show any signs at the house of having a daycare inside. I know it's hard sometimes, but I don't have a sign up.

It does sound like someone trying to stir up trouble.

I would just ignore it. Nothing will come of it. And if something does? oh well... you weren't doing anything wrong. You have nothing to hide.