Crazy quilt blocks sounds good. They also might like to watch you sew the Disappearing Pinwheel blocks. They might be surprised as you sew the pinwheels and then cut them again with your rotary cutter to make the two different block arrangement.
They also might like a simple snowball block but kick it up a notch with markers. Do the snowball in bright yellow and have them put different smiley faces on them with markers. It would also make a cute hall quilt to hang in the school with all the different expressions. You could print out a bunch of computer emoticons if they need ideas.