Hi! My Mom is a weaving guru!
You can make a peg board and weave yarn onto that to make pot holders or squares for scarf, vest, blanket, etc. Or make/buy an apache loom to weave small blankets and wall hangings etc. Really really simple, you can tie fabric strips to the back of a cane chair and then weave in other rag strips for a cool rag rug. And another nice idea is to make tiny 1" to 3" sqares with yard or fabric strips and glue them onto cards for thank yous etc.
I dont know about books, but there are a couple of magazines that have beginner projects that could probably be modified for a toddler/preschooler too. Weavers is the only one that comes to mind, but I know there are others.
Good Luck and Have Fun!!
ps. My mom's website is http://www.weaveit.com
-- Just to brag. I dont think there is anything a toddler or preschooler would find interesting about her pattern software...
But maybe for inspiration?