Did you watch the video? Her expressivity and musicianship is far beyond many adults.. She had also just finished a concerto playing with an orchestra

EDIT Also with band music or non-classical music so much of it is to do with platform and distribution, and 7 year old prodigies don't get much interest outside of talent shows or Youtube. Justin Bieber (as mentioned in another reply) though is a good example of someone who did at age 12