You can get it nboted on your dining reservations that you are celbrating their birthdays. Many of the table service places do decorated cupcakes and a few also sing Happy Birthday. The boys can get a birthday pin when you check in and if they wear it, they will get lots and lots of "Happy Birthday"s from CMs and characters. Last week, my older dd wore her most of the day, my younger wore her the first 2 days. It was noted on all dining ressies and we just enjoyed whatever attention they got.
I remember cupcakes (or ice cream with a candle) at :
Chef Mickeys
Cape May Cafe (Goofy also conducted everyone in a Happy Birthday song for my oldest, one of her favorite trip memories)
Akershus
Sci Fi
The Plaza (they got sprinked with confetti from the Mayor's friend there too)
CRT
H&V (breakfast)
Tusker House breakfast
also, a cute gingerbread cookie and tink clip in Biergarten
Also, a few gave them birthday cards signed by characters or staff. The best card was Biergarten where they wrote Happy Birthday wishes in both German and English and a bunch of the staff signed it. Biergarten was the best, IMO, at the celebrating overall.
Oh, and at Mama Melrose the girls got a paper chef hat that said Happy Birthday which was perfect because they were too full for dessert, LOL.
Nonfood, but in AK during the parade, many of the performers said Happy Birthday to them during the parade. Also, we got to ride RnRC an extra time without waiting because dd* was wearing her pin.
Oh, and a photopass CM sang to dd5 on the street in DHS when we chatted and I mentioned that dd8 had been sung to at WDW but dd5 had not (I wasn't complaining, he had asked if anyone sang to them).
eta: we never paid anything extra for any of the birthday stuff. It was awesome and we were happily surprised each time.