Holy Moly! Comes to us from the Lutherans and could quite easily serve you well in a multi-age classroom setting. Click on the link here to further explore Holy Moly!
Small Churches - These lessons can be taken directly off-line. Newly revised in 2003, all the Sundays for Years A, B, and C are now available, following the Episcopal lectionary. There are specific lesson plans for young children, older children, and adults that include ways to tell the Gospel story, activities and questions for discussion.
Abington Press
One Room Sunday School (Abingdon) is a Methodist curriculum developed for small churches where many ages are combined in one class. Quarterly packaged material makes teacher planning very easy.