Hi Stacey, I can understand your desire to keep your family all together. With 5 children myself, I know how hard it is to find accommodations that can fit you all.
Technically, the person who told you that is correct. You
can request a cot and use the trundle bed. However, this would be for situations where 2 of the kids won't sleep in a double bed together (brother/sister, etc)...and it would make for a tight fit. It is also possible only when it won't put you over the maximum allowed per room. At Port Orleans Riverside, the maximum number of guests in a trundle bed room is 5. This is a safety issue (fire code) and they won't make exceptions. Even if you tried to put 6 in there, you would only be able to register 5 family members. This would mean that your additional child would not be on the dining plan, would not have a Park pass and would not be able to participate in Extra Magic Hours (as they need to show their Key to the World Card for this benefit).
Have you considered the Fort Wilderness Cabins or the All-Star Music Family Suite? These both sleep 6 people. See:
HERE for the Cabins and
HERE for All-Star Music.
I hope this helps and that you are able to find a way to make it work for your family. Let me know if I can help you further.
Kaylene