It really depends what they are looking for. We've had a birthday dinner at California Grill, they just put sprinkles on the table, but the setting is so stunning and the food so good that is fine. However, you would be lucky to get a reservation now, especially with the 24 hour opening at MK. We had a fun birthday dinner at Chef Mickey, they gave birthday diners different colour napkins which have to be waved at various poiints during the evening - and make it easy for the characters to recognise the celebrators! Also badges and cupcakes, my daughter is grown up but we had a great night.
I'd advise them to book asap though!