Someone else will be able to give you specific replies, but just to share a couple of tidbits. At many TS places kids (big and small) get a cup cake for their birthday. My nephew got a cute one with a plastic Mickey face at Chef Mickey's. With the buffet spread there a cake would have been a waste for us.
You also have the option of ordering a 6" rather plain cake at the podium of the restaurant when you arrive for you ADR. Cute and tasty, but not the artwork you want. Last year those things were under $15, now I understand they cost over $20. I kept trying to justify buying one of those, but I couldn't and we were never short of sweet options at WDW!