Chef Mickey's and an adult birthday somehow don't jive well with me. Thinking about that place gives me a headache, and an upset tummy.
I'd suggest a couple differnt things. The California Grill and Narcooses are both lovely and offer a fairly sophisticated menu with a fireworks view. Both are family friendly nad also have a childrens menu.
Another option might be Boma if the adults are adventurous eaters. It's less expensive than the first two ideas, and is a buffet with something for everyone (unless someone has food allergies, then stay clear). There is also a kids buffet with the standard issue kids stuff. The nice thing is that kids can try items from the rest of the buffet, giving them the opportunity to sample without worrying if they don't like it.
Any WDW restaurant can provide a cake if you call ans speak to them a few days in advance. Depending on what you want, they may or may not chanrge for it.
Have a great trip!
Anne