A big 4 patch is easy to do - easier than a pillow case. My niece and nephew were 7 & 8 respectively when they sewed their first quilts. The 4 patch gave them an early success. Their quilts were baby size, but done in fabrics of their choice. They 'shopped' in my stash for their fabrics.
The kids also liked using the "fancy" stitches on my sewing machine for the quilting - after I anchored the sandwich with basting. They were very happy with the fruits of their labor! Me, too, as it helped them get through a rainy weekend!
Have fun!