I remember learning German through reading some children books. I really liked the Asterix books

http://www.thegermanproject.com/stories

Here you go - they are free (they are for young kids, though).

http://www.childrensbooksforever.com/childrenpages/German1.html

Amazon has Harry Potter in German. I'm sure other sites do as well. When looking for stories etc. Do the search in your target language, and you will get better results. For example I search for "histoires français".

How about some traditional German fairy tales? As they're short they tend to be easier to bite off than a full novel. Some of the vocabulary can occasionally be a bit obscure and old-fashioned but they're well known tales which might make them easier to follow.

To get you started, here's a link to a free kindle version of all the Brüder Grimm stories. If kindle's not your thing there's plenty of other versions online (they're out of copyright due to age): https://www.amazon.co.uk/Kinder-Hausm%C3%A4rchen-German-Br%C3%BCder-Grimm-ebook/dp/B00ANU7OO2/ref=sr_1_1?s=digital-text

Pretty much anything's available in German. Just pick something you enjoy and read the German version. Of course, you'll want to look for simple and contemporary language, so comics or something like Harry Potter works well. There are many tales and fables too, but those are often written in a somewhat archaic tone.

My favorite series ever is "The Queen's Thief" series by Megan Whalen Turner. The first book in English is titled "The Thief." The German title is "Die Legenden von Attolia: Der Dieb." Even is you don't get around to reading the German version, I highly recommend picking up the English one.