I have found an interesting article by Zoubeida R. Dagher and Danielle J. Ford about children's biographies of scientists ("How Are Scientists Portrayed in Children's Science Biographies?", Springer 2005), with an excellent critique of children's biographies of scientists. Immediately, I noticed that there are many similarities with Christian biographies. For example, the characters are usually represented as heroes and lone rangers (working independently from the scientific community and previous research) and relying on observation rather than methodical study.
One sentence in particular, regarding a biography of Galileo, struck me. "There is no hint to the complexity of Galileo’s proposal, suggesting that any person should have been able of looking carefully through the telescope and seeing what Galileo saw." We do this so often in Christian biographies for children! I have read some children's biographies of Luther that have left me with the feeling that anyone could have opened the Bible and discovered justification by faith! There was no mention of the work of others before him, both as individuals and in church councils.
I have already turned in my biography of Athanasius, but until the editor sends it back with their corrections I am still keeping it in the back of my mind to make sure I explain to the children the complexity of the Arian controversy rather than just giving a simple good guys vs. bad guys account. It's not a matter of complexity or simplicity of language. I think it's a matter of mindset. If I see the issues in simplistic terms, my books will be simplistic. If I take time to understand the issues in their historical and intellectual context, my words will reflect that, while remaining simple. The more I continue to read and understand, the better the end result will be. It's the same when writing historical novels - if I pick up a few details about the time period and insert them here and there, the artificiality will show, but if I soak my mind with a great variety of pertinent information, then as I write the images will appear naturally in their proper context.