The American Music Therapy Association, or AMTA for short, is the go-to resource for everything related to music therapy and is the organization that unites music therapists in the USA. There is a vast body of information related to the use of music therapy with different populations including but not limited to children in the special needs community on this website.
Music and Child Development Resources - our partner, The Music Place's, list of resources for making practicing music fun, interactive websites, games, tips for getting started for the beginning musician, plus many more.
Scribd - great sheet music resources for tablet users, contains a vast collection with various genres and instrumental arrangements of music. This is a paid subscription service but has a free fourteen day trial.