Recently - while reading this compendium of Christian theological propositions - I began thinking about theology for children and the resources available to teach them in a systematic fashion.
In due course, I ran across some good resources that I wanted to capture - see below for some results.
I pray these are helpful to you - please feel free to post additional sources in the comments section.
Catechism for Young Children
Catechism for Your children
A small Reformed catechism for Preschoolers with Bible verse answers
The Small Child's Catechism
The Westminster Larger Catechism, part one
The Westminster Larger Catechism, part two
The Westminster Shorter Catechism
The Westminster Larger Catechism with proof texts
The Heidelberg Catechism
The Center for Reformed Theology and Apologetics
Fisher's Catechism and the catechism of the Church of Geneva at this site, but because of the way they are set up, you need to go the main page (which is a frameset), navigate through "historic church documents", and scroll down to the section on catechisms to read them.
Scroll down for Luther's Large and Small catechism
For Reformed theology, the Small Westminster Catechism and the Catechism for Young Children are both sold in a nice workbook format put out by Christian Liberty Press, likewise, Covenant Home Curriculum offers a "package" for teaching the Westminster shorter catechism which includes several teacher's guides and explanatory books, as well as a daily lesson plan for dialectic stage students.