@Gary412 I too, have a "no kids" rule but one of my very first few guests inquired about coming to stay with a baby (I think about 6 months as well).
She inquired in a very polite, friendly manner explaining even though she filtered for kid-friendly, my listing still came up and would I be open to hosting them anyway.
Because she approached it this way, I told her yes. But I explained that my house is NOT child proof and I had nothing to offer for babies/children (and they would have to bring anything they needed) and that also the room might be a tight squeeze with a playpen/crib.
She was fine with that and they ended up being fantastic guests and I received an excellent review. I still have a "no kids" rule and haven't run into the issue again, but if the guest is friendly about it and seems reasonable, I wouldn't have a problem with it again. I don't necessarily see this as an opening for a guest to break more rules. It's all in the approach.