Can I choose what area I want to work on in the job interview? For example I want to work on child care floor as a CNA

Unfortunately you usually don’t have a choice as a cna.Perhaps they would transfer you there when there is an opening. In the meantime take any course you can related to specialty . Pediatric cpr, etc. this might help boost your resume. Also volunteering in that area can give you experience in what you are looking for. Good luck!