There are a lot of great book series for 13 year olds. Some of our favorites include the Harry Potter series, the Percy Jackson series, and the Hunger Games series. However, there are many others that are also great options. It really depends on what the child is interested in. If they enjoy fantasy, then the Harry Potter series is a great choice. If they enjoy adventure, then the Percy Jackson series is a great choice. And if they enjoy dystopian fiction, then the Hunger Games series is a great choice. There are many other great book series out there, so it really depends on the child's interests.