Hello! I was wondering what exactly do you get if we dine there for someone's birthday.

If you registered for the Aloha Club, you're supposed to get a free entrée plus a slice of cake.

Yes they bring out a slice of cake, and sing

That was my experience, when I was at a kids BD. Since they are also a bakery, i would imagine you could substitute, an equal bakery item.

I think they might bring out a slice of paradise cake. Though I'm not sure.