Research
The field of Music and Childhood Development is vibrant and growing. Here are some web resources to get you started (more to come, stay tuned..):

The Childrens Music Network - http://www.cmnonline.org/
The National Association for Music Education - http://www.menc.org/
Zero to Three - http://www.zerotothree.org/
Hap Palmer - http://www.happalmer.com

Book List:
Movement That Fits: Dalcroze Eurhythmics and the Suzuki Method
by Joy Colin Yelin

First Steps in Teaching Creative Dance to Children by Mary Joyce (for teachers mostly, forward by Ken Guilmartin)

120 Singing Games and Dances by Phyllis Weikart

Life Drumming, an essay by W. A. Mathieu

Music Together® Questions and Answers