Here's an easy and inexpensive way to create bookshelves that are ideal for kids: rain gutters. The Raising Olives blog features a tutorial for this popular project, which can encourage children to read more.
Rain gutters are sturdy and take only a couple of hours to install, plus the total cost for a few shelves is probably under $50. With the book fronts facing out, kids are more likely to read more -- and they can get and put away the books themselves.
You can see the step-by-step instructions in the blog post below. (An even cheaper idea which requires no sawing is to use IKEA spice racks, but the gutters give you a more custom wall-to-wall look.)