She's set as child because 12 isn't technically teen. She is one of the most interesting characters and has a more of a teenage voice. Shadow is 12 years old and is the Elemental of death. She voice is kind of protective and a bit flat (Think girl Nico if you will. Ok I'll shut it now). She starts off as a closed off and kind of mean character at the beginning of the movie. She later gets more kind and friendly, but is still closed off.  She has a twin sister that she hates like hell. Her twin is Ashanti, Elemental of weapons. Ashanti killed their parents to get to Shadow and the twins have a dark history that unravels. She, Piper and Ashanti are the only ones who can travel to Earth. She's a part of the Natures, but later leaves it to become the Queen of the Underworld.