Originally Posted by
Dsm2m2
As long as you are still within a refundable period, I would always recommend to book first (in this instance 2 adults only) and then call to make modifications.
"Hello, I just received my email confirmation and realized I forgot to add a child to the reservation. Is this something you can modify for me?"
I can almost guarantee that's not going to work. You will need to talk to the HOTEL, not customer service. Customer Service is just going to say "The occupancy is only listed as 2, you can't book it for 3, would you like me to cancel for you".
You'll want written confirmation from the hotel saying that it's ok to have a child as the third person and that they will accommodate with a rollaway/crib/whatever.