Ok now HERE'S an example of something quick and easy that you can put together in a weekend. All it takes is some 10"-12" wide x 1" thick lumber (actually, this one took a LOT, to the tune of 24'...), 12' of 5" x 1", a 4' x 4' project panel (1/4" thick is what I went with), and some paint.
Does this HAVE to be a kids' room bookshelf? Absolutely not. Actually, if I had stained it instead of painted, and perhaps made the trim details a little less "whimsical" at the top, it could easily have gone into the living room. This thing is SOLID, it's made it through 3 moves (one cross-country!).