I have heared the opposite advice so often, I‘ve lost count. And I really enjoyed picking some really nice books to read them to my now twelve year old son. What I pay a lot of attention to when choosing a book is the language. They are lovely written and it was a pleasure to read them to my boy but the language in there was everything but simple and definitely not suitable for a beginner but rather for the very advanced learners.
Oh, they meant those ,other‘ children‘s books. Where Timmy and Tammy ride the ponys to candyland. Well, hum, really? Would you read that in your own language? I mean by yourself? I‘m sure your intellect rejoices when you flip the 2inch thick pages to see those lovely drawn images with that one or two lines of literature written under them? I mean, who wouldn‘t (at the age of two)? Either way:
They are not for You
Well written children‘s books use a language full of the written past tense called Präteritum. It uses antique, low-frequent words and non-communicative structures. They are literature. Ever met someone speaking like a book? Books made for toddlers are an insult to the adult‘s brain that is capable of so much more than to read ten sentences (that you should be able go over on a single day anyhow) about construction-vehicles, firemen or Dolly‘s first day in school.
Do what you love
If you like to read, read what you‘d normally read. Even if that means not understanding major parts of it. But at least you are directing your interest towards your interests and pre-knowledge. Read it online with a good browser dictionary and you will quickly get the idea of the article or text. You will forget the words and structures that you don‘t use in your everyday‘s life or at least park them in the darker lots of your memory where they will become dusty and rusty and finally die, sad and alone.
Great online dictionaries are linguee.com, dict.cc, leo.org or pons.de. Or search for ,browser dictionary plugin‘ to make finding words even more comfortable. Finding German sites that contain information about your field of interest shouldn‘t be a problem either.
Learn German like an adult, like an individual that wants to share what he or she has experienced and learned.