My wife got a cake, birthday card, balloons, party hats and noise makers at the Polynesian (GV, not concierge) for her birthday 2 years ago. When we checked in, the CM asked if we were celebrating any special occasion. I mentioned that it was my wife's birthday that week.
Last month, again at the Polynesian, my 2 boys got balloons, autographed pictures from Mickey, sand pails full of goodies, and coloring books. It was not their birthday, I didn't ask for anything special, no special occassion. BUT, I did tell the CM, in response to his question at check-in - "Is this your first time staying with us at the Polynesian?", that this was our 8th vacation at the Polynesian and to please put us in a nice room.
Even though we've had some nice surprises on 2 of 8 stays, I agree with others and say that if a birthday celebration is important to you and you don't want to be disappointed, call and make arrangements through the Disney Florist.