child asking about if you'll have another baby?
I don't see anything wrong with your child asking if you'll ever have another baby. Kids often ask these type things for a myriad of reasons, like: maybe they are curious if they will ever have to share daddy with someone else, a mild jealousy thing, which is natural, also, they may wish they had someone to play with, and many other possible reasons only your child would lnow or feel.
I would not worry about this whatsoever, and I would simply answer them in total honesty. After all, what's the matter with honesty? Kids will understand, believe me. They are capable of dealing with things much better than we give them credit for, as long as we are honest. I'm a firm believer in that honesty truly is the best policy.