This can vary according to the craftiness of your young ladies to start with. You might have to start with basic cutting with scissors for them. jollyquilting's idea of rail fence blocks are easy and allow for color matching if they want. you can increase the strips to make a bigger block, and it will take less blocks for them to have to sew. Or a four patch block can be any size and takes two fabrics per block. It can be scrappy. Charms are good for this.
You can teach them to strip piece or the block method.
If you have machines to sew with, you might want to spend time with paper drawings to have them practice guiding the paper to the needle.