This is a series that I loved as a kid. It's about Princess Magnolia, who seems like a very proper, “pink loving” princess, but she is actually a superhero in disguise. Her alter ego, the Princess in Black, does all the things a traditional princess “isn't supposed to do”.  She fights monsters and even wears black.

This is a great book to teach little girls to break simple stereotypes and how assuming things about a person is never a good idea. The monsters the princess fights are also really funny as is her horse, Blacky (or his alter ego, Frimplepants the unicorn). This is a really fun book that  kids starting chapter books will love, especially if they like funny stories or princesses!