We took our oldest daughter to WDW when she turned 4...it was great.
First go to Town Hall on your right when you enter MK & tell them it's her birthday. They will give her button that says "today's my birthday" which she can wear all day. (My DD wore hers all week!)
Sometime when CM's see the button they will bring the child into the parade. My DD got to dance with prince charming in the older parade (the one before the water globes).
We also did CRT for breakfast...The prince picked up my DD & asked her "what did Mommy & Daddy get you for your birthday?"..she replied "nothing"...we all laughed!
When we stayed at the Poly upon arrival we were greated to a cake & balloons in the room.
Have a great time. Disney is the best place to celebrate a child's birthday. JMHO.