The Internet offers a large number of free resources that can be used to study the Bible. You can find workbook activities, Power Point presentations, Bible games, even studies of each book of the Bible with accompanying activities and puzzles. This age group responds best to activities rather than lectures, so find ways to engage their minds to make the lessons stick.
This site provides a series of lesson plans that also include activity sheets to support the lesson. For example, the lesson on Luke 2:41-52 is an inventive look at Christ's "family business" and how we can all be part of it. The lesson includes the printable full lesson but also includes a downloadable PowerPoint presentation (you will need PowerPoint 2007 or later as these are ".pptx" files) and worksheets. The site also has a Bible Study Blog that provides ideas for other lessons and activities.
Children's Bible Study
Christian Teen Shop
This site provides a more traditional set of workbook pages with a full lesson plan that includes fill-in-the blank and short answer worksheets for each lesson. It also includes memory card work sheets and a number of puzzles that use the lesson material.
The Problem of "Free" and "Online"
It is clear that an online search for "Bible activities" will turn up hundreds of thousands of hits. There are a large number of opportunities that can be used by the careful teacher. Most sites will try to sell a product but will provide free material as a "loss leader." If the free material is working with your class and the costs are not too great, ordering the full set of material may be worth it, but always experiment carefully first.