The following papers provide useful information about the development and properties of the Spence Children's Anxiety Scale:
Spence, S.H. (1997). Structure of anxiety symptoms among children: A confirmatory factor-analytic study. Journal of Abnormal Psychology, 106(2), 280-297.
Spence, S.H. (1998). A measure of anxiety symptoms among children. Behaviour Research and Therapy, 36 (5), 545-566.
Spence, S.H., Barrett, P.M., & Turner, C.M. (2003). Psychometric properties of the Spence Children's Anxiety Scale with young adolescents. Journal of Anxiety Disorders, 17(6), 605-625.