These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
The descriptions of the Fire-us pack a pretty impressive punch, considering how short they are.
And The Kiln gives us the charming revelation that babies born after the Fire-us are being burnt alive by the Keepers of the Flame.
What Do You Mean, It's for Kids?: It's a trilogy of young adult novels full of terrifying mental illness, a Christian cult that wiped out the entire population of America and probably the world, The Talk and at least one glossed-over mention of male genitalia, and of course the scene in the last book where you find out that President has been collecting children born since the Fire-us and burning them alive in a quest to find the Messiah.