I like the charm packs for kids to sew. They even make a sudoko quilt kit.
I would suggest having the fabric cut before hand so all they have to do is sew.
Put a pile of post it notes with a large rubber band or tape them down so the seams are all the same. The kids butt the fabric up against it and the seams are. My 6 yr. old son says put the stack next to the right side (1/4" inch seam) then let her sew at the slow speed, not to fast or she could get hurt.
He likes the cotton batting- spray baste and let them quilt in straight lines.
Nessie: Have fun.