Hi, Alba. Congratulations on your book!
Unfortunately, there's no one easy way to promote. You might consider putting the book in KDP Select and running a short initial giveaway. That's a good way to start generating reviews. You can also do a giveaway through Librarything. If you make a paperback, you can run a giveaway through Goodreads. Submitting your book to book-review bloggers who review self-published kids books is also a good idea, though you can expect to get a "no" or no response from many of them -- they're all overwhelmed with submissions. You can also begin building a social media presence (your own website, Facebook, Goodreads, Twitter, etc.), though it will take a while and a fair amount of time on your part for these to bear fruit. If you find discussion forums dedicated to your genre, you can join and participate as a reader (don't explicitly self-promote). Once you have some reviews and a feel for things, you might buy paid ads. They work well for some folks; others have found that route unproductive. Hanging around here is a great way to gather information about advertising venues (and much else).
Here's a thread that collects a ton of great "getting started" links:
http://www.kboards.com/index.php/topic,111778.0.html Many won't apply to you, but you might find some useful.
Good luck!
