OP here
I just wanted to say thank you for everyone's comments and concerns. I spoke with Disney's guest relations this afternoon. I have my son listed as 3 on all of our dining reservations and our airfare. The rep. that I spoke with told me that they would have to review things, and then they would call me back. About two hours later, they called me. I am guessing that they were reviewing our origional phone conversation.
Long story short, I was very polite and stated what I wanted resolved. When they called back, they told me that the difference would be $342.54. They said that since the error was on their end, they would take it down to $142.54. I told them that sounded fair, and I will pay the difference.
Thanks again!