I know MK, maybe all the parks have a pin/button at guest services that has all the characters on it and it says, "Today is my Birthday". the CMs throughout the park supposedly see it and wish the child a "Happy Birthday".
When I was standing in line to get one for DS8, I think another child who was actually in line (mine waited outside) received a phone call from one of the characters...
If you are staying on site, call the reservation line and inform them that you have a birthday child. They will make a note on your ressie. Then when you arrive, remind the CM at check-in. They will arrange to have a couple of balloons and a card from his favorite character waiting for him in the room. They were very accomodating for us, we were there on a b-day trip for DS8 and DS6, but it was only really DS8's b-day. I explained all this, and they arranged for both boys to receive balloons and cards..
these are the freebies that I know of. We were too busy to arrange any special reservations or cakes or anything else. You may want to post your question on the resort board or the attraction board-I am sure you will be over loaded with things you can do.
Have a great time!!