I had the same experience at the Vancouver Residence Inn - an email to the GM confirmed they do not charge for children, despite the website showing otherwise. So as a result, the Marriott booking engine is potentially either charging some customers extra or sending them to other hotels because they don't want to pay a fee that the hotel isn't even expecting.

It would be nice to hear from a Lurker as to what the actual policy is for children. I don't like having to waste time contacting hotels directly, especially then the emails have now been concealed.