I noticed this same thing with the Renaissance Bangkok. They show max occupancy of 2 in the rooms (where you can get 2 x double beds) and the ability to add a rollaway bed. So 3 beds, but max occupancy of 2. But when I went to booking.com or some other site, when I selected the same room, it showed 2 + 1 child under 12 years old. I really dislike the difficulty in finding details for how children are handled - it can be anywhere from over 2 is an adult to over 16.