Reddit mentions of His Dark Materials 3-Book Paperback Boxed Set: The Golden Compass; The Subtle Knife; The Amber Spyglass

Philip Pullman's series, His Dark Materials is perfect for that age.
http://www.amazon.com/Dark-Materials-Yearling-3-book-Boxed/dp/0440419514

Pullman also wrote books about a female detective in the Victorian era in England that are great. But I think the Dark Materials are probably closer to the Hunger Games experience with strong female characters, adventure and excitement.

http://www.amazon.com/Ruby-Smoke-Sally-Lockhart-Mystery/dp/037584516X/ref=la_B000AQ74C6_1_6?s=books&ie=UTF8&qid=1404849661&sr=1-6

I also used to read Juniper and Wise Child over and over as a kid. Really engaging and well written. There is magic in the book, but not in a silly way. It's based on Celtic healing and religion so it's not like dragons and fantasy magic. Fits again with the strong female characters.

http://www.amazon.com/Juniper-Monica-Furlong/dp/0679833692/ref=pd_sim_b_1?ie=UTF8&refRID=04QZXYYBRNN5R5Z0M1TY

http://www.amazon.com/Wise-Child-Monica-Furlong/dp/0394825985/ref=pd_sim_b_1?ie=UTF8&refRID=0JB52BH5DD07Y58DTS7C

It also looks like there is a third book, but I never read it!

Philip Pullman's "His Dark Materials" series is the first thing that comes to mind

Also any book or series that approaches the world for a rational, scientific perspective could also be considered to have an atheist subtext I suppose.

Do you want His dark materials or Book of dust?
This is HDM
You can choose: https://www.amazon.de/gp/aw/d/1407135597/ref=tmm_pap_title_0?ie=UTF8&qid=1558372819&sr=8-1
. https://www.amazon.com/Dark-Materials-Yearling-3-book-Boxed/dp/0440419514
. https://www.bookdepository.com/His-Dark-Materials-Philip-Pullman/9781407131184