In my experience it's fairly dangerous to allow infants to a listing that is not equipped (for example, with cribs). For example, if you have a room where maximum occupancy is 1, then in theory they can still tack on 2 infants onto that, making it 3 and making it the worst nightmare lol.
This is why I have it expressly written into my house rules that infants are not allowed. Now Airbnb can't do this since it would be discrimination as they did used to have a section where you could select whether or not to allow infants or not but later took it out!
Although yes we did have the worst possible scenario happen to us where a family of 5 booked our room for 2. 2 adults, 1 younger child, and 2 infants, all trying to cram into 1 single queen bed lol. After that we know that we can not allow infants.