How do I become a twelve yr old actress?

You need to join local community theatre productions. There are often parts for young people in adult productions and most cities have youth theatre groups. Ask your English teacher at school about how they think you could get into youth theatre. Join a choir group to learn to sing in tune and in harmony with others. There will be youth choirs in your city. They will help you to work out what your singing range is and whether you have a talent for singing. To be a professional actress, you will greatly improve your chances of work if you learn to sing, dance and act. That is called a triple threat (meaning that you can do it all) and means that you are more versatile and can do a range of acting jobs. Very few people make it as a professional actor without proper training. It is very competitive but start now and you will build up the skills you need. Chase your dreams and best of luck!

Take advantage of every opportunity to act that you come across. Audition for school plays, community theater etc. Those are generally free and will give you great experience if you want to branch out into tv and film roles. Ask at local hospitals, sometimes they need people to act as patients to train medical professionals. Get together with a group of friends and volunteer to act out a children's story at your local library.

Work on the talents that you do have and make them better. If you have any distinguished features like curly hair, don't try to change them. Stand out from the crowd but don't be afraid to be different. Be confident and optimistic more than anything! Going on pantomimes and trying for the lead roles, you prob wont get them at 12 but you can always try. These things will build your confidence and stage presence.