At the entrance of each park, visit guest relations and tell them it is your B-day. They will give you a "Today is my B-day" button. You will be surpised all the things you get (especially the kids) and the birthday wishes. At hotel check in, tell the front desk you are there to celebrate your child's B-day and their favorite character. THey will likely send balloons to your room and have the character call the room to wish him or her a happy B-day. Just a few thoughts that worked for us...one other thought, most of the restaurants will offer a B-day cake (which you have to pay some good money for) but could be nice. You also could call ahead for a personalized B-day cake for your dinner ressie. Last year, we had dinner in MK at the castle and called in advance to have personalized cake. If you are going to a special meal or character meal, they will also make a big deal especially for the kids.
Hope this helps. Have fun.
