Does he have a favorite character? My first thought would be chef Mickey. I think another one, that does not actually have characters but a six year old would love is whispering canyon, all the antics make kids really love the place. Not sure about any others, one of my problem is we have all girls, so I'm not sure exactly what boys love, but I know our 4 yo loved chef Mickey, and she has always loved whispering canyon. The only other one she loves is 1900 fare but that is Cinderella also. She is 11 this year and wants afternoon tea for her special time. Just one other thought, I don't think anyone does birthdays up big at Disney, because they have 15 every hour or more, so I think it's more you at the table, family and friends. Disney will send over a cupcake, but that's about it, oh some ts do send over a card, I remember Tucker's and cry doing this, don't remember which other ones do.
Sometimes the resort does something special. We stayed at por when she turned 3, everyday for a week when in the lobby, she would dance around and say is it today I get to dance with the prince and she would start dancing and staff all got into it. Well when the day came, I walked thru lobby and when she asked I said after your nap you will dance with the prince. Two hours later we got a knock at the door from a doorman, who in rolled the scroll and read that she was invited to the ball by the prince. She to this day remembers the special invite with gold lettering and she did get to dance with the prince that night. I have never heard of anyone else getting this treatment, but it was special. We did have a friend working at Disney but she swears even now she had nothing to do with it.