If none of these kids have every used a sewing machine, I would have them just putting alternating blocks together. For my daughter's girl scout Silver award I taught our girls how to quilt as well. My girls were in 9th grade. Some of them had a tough time trying to sew a straight line, much less a consistent seam allowance. Each girl pieced together 2 baby quilts that we were able to donate to mom's at a public hospital. While the girls did the piecing, I quilted each of them and did the binding on them.
Before having the kids start stitching directly on fabric, you may want to draw some lines onto blank paper and have them trying to stitch along the lines without thread. That will help them get the feel for how fast or slow they need to sew.