Elementary Theory of Music: A Reference Book for Children is a book written more than 100 years ago. This small book was published in 1913 and was written by Mary Reston Black & Margaret Bell Black. Elementary Theory of Music was chosen for three reasons: 1) its subject matter (music), 2) its brevity and 3) its public domain status.  
As a musician myself, I decided to develop a self-contained digital, multimedia educational solution. This eBook is intended to provide an introduction to learners of all ages. Music is by nature multimodal, and requires that learners are engaged not only in writing but also with aural and kinesthetic approaches.