Uni the Unicorn in the Real World by Paris Rosenthal

Uni the Unicorn, the only unicorn who believes kids are real, slides down a double rainbow to visit friends on earth. Uni the Unicorn visits her best friend in the real world. Now everyone will know that unicorns exist, and that Uni is real after all. But when the little girl introduces Uni to her family and friends, they can't see the unicorn. Then, with the power of believing and Uni's magic horn, one little boy begins to see something. And then all the kids begin to believe in magic. And as the real world grows brighter and brighter, all kinds of other magical creatures appear, ending the book with the most dazzling array of imaginary creatures. Paris Rosenthal, the daughter of the late Amy Krouse Rosenthal, wrote this as a tribute to her mom.