A friend who has an incredible ministry and heart for children and the church has written this section.

Children Matter:  Celebrating Their Place in the Church, Family, and Community by Scottie May, 2005.

Children Mean the World to God by Harold Shank, 2001.  A good theology of children.  Shank uses a lot of scripture as its base and deals a lot with disenfranchised children.  Very reader-friendly and has some exercises at the end of each chapter that might be good for group discussion. 

Family the Forming Center:  A Vision of the Role of Family in Spiritual Formation by Marjorie Thompson, 1996.  Some of it is pretty thick (especially at first), but it progresses to give some good, practical ways that families can be the primary spiritual teachers of their children, including some good stuff on family rituals and celebrations.  She comes from the perspective that
Joining Children on the Spiritual Journey:  Nurturing a Life of Faith by Catherine Stonehouse, 1998.  Stonehouse sees us as "pilgrims together on the journey".  This is an easy read.

Postmodern Children's Ministry:  Ministry to Children in the 21st Century by Ivy Beckwith 2004.  A very good resource.  She has chapters on characteristics of the postmodern child, the role of the community of faith, children in worship, etc. 

Real Kids, Real Faith:  Practices for Nurturing Children's Spiritual Lives by Karen Marie Youst, 2004. This has lots of practical information and things that parents and children's leaders can do to nurture children's spirituality.  Reader-friendly.