I've made pinwheels in colorful kids fabrics, or simple blocks using I spy fabrics. I also made a double Irish Chain that turned out really cute using pastel fabrics for the chain with small appliques of ducks, stars, moons, and other assorted kids things between the chains. For something really fast and simple the panels are great or get a themed kids fabric and fussy cut for centers of blocks with simple borders around each block. So many possibilities. Do a google search for free children's quilt patterns for lots of ideas.