They are small but I would think they are big enough for a 5 year old, it should be just perfect for your 3 year old. I actually got to see one on the hallway to my room.

Hello, sometimes is a big issue when traveling with large groups that are border line to the capacity, I would suggest to call the hotel and talk to the people in front desk and ask by giving details, since the double room is big enough for four adults just request a crib for the little one. I personally think you should be perfectly fine. Again, you can call the hotel and make sure you write the name of the person that’s helping you out before making the reservation.