Generally, the baby doesn't "count" until they need a bed of their own. Some state an age. Some go by the above. So I did what the pp does. I email the hotel property directly to ask for the extra bed/cot. Once in Spain, they emailed back no. There's no room. They weren't kidding. We solved that one by changing the size of the other room (we're 5 and needed two rooms) so when I saw it, they weren't making up a story. These was no room for an extra bed or even a folding cot.

FYI, I've been refunded completely every time. Booking.com is good for this.

Some of the rooms in big cities in Europe seriously have a crawl space around the bed. No more. In Geneva, my uncle and his wife showed me their room and really, no baby would have fit, even a 5 month old. I know that as a single Flight Attendant, we often got these rooms and space was at a premium.

Cosleeping is fine for many families but remember that in certain parts of the world, the beds are smaller. They sometimes sell a room for two with a 140x160cm bed. Is this a double in the U.S.? If you cosleep, always ask the dimensions of the beds, especially for big cities and/or abroad.