A.
I disagree with the person that said you shouldn't use diapers at night. That advice really only applies to day training. As someone else said, you can't really night train - the body is either physiologically ready, or it's not. It's not a conscious decision.
My daughter is just now night trained, and it happened at about 3.5. BUt, I actually think that was somewhat early. She went from being very wet every morning (even going through diapers) to being dry every morning in literally a few days. I think you'd be hard pressed to find a pediatrician that was concerned about a 3 year-old still being wet at night. Not to worry!