I started several young kids on quilting by helping them to make Project Linus quilts:
Select a fabric that has a panel, or stripes or blocks and make a quilt sandwich. Baby fabrics often have designs like this. Have the children sew on the lines with a walking foot. It's kind of like driving a car, staying on or between the lines. The fabric we chose to start on was Phoenix Suns motif with lots of white lines in a grid and basketballs in the little "boxes." The kids learned very quickly how to stay on the lines, and they ended up with a quilt that just needed binding.
This is not a pieced quilt, but for a first project it was fun, and was about giving to others and learning to use the sewing machine. Because it was already a quilt sandwich it worked up quickly. Both girls have gone on to make other quilts made with charm squares and a simple border. The charm packs are fantastic in that they offer lots of pretty fabric choices and there is no need to use a rotary cutter. The kids loved arranging the charms into a pleasing design. One made a gift for her mom and was so happy to be able to give it to her, something she had made herself.