DW cried when Dumbledore died. DD at 6 barely blinked. It's all individual.

For parents concerned about their children's emotional response, Book 4 is the watershed, as that's the one which culminates with a child murdered.

DS8 just finished the first book in the Redwall series by Brian Jacques and loved it. We learned there are numerous books in the series and have just requested three from the library. I didn't see this series on the list.

I've added it - thank you!

Primates: The Fearless Science of Jane Goodall, Dian Fossey, and Biruté Galdikas, by Jim Ottaviani & Maris Wicks.

It's in graphic-novel format and appears to be aimed at an adult audience (e.g. it mentions Louis Leaky's philandering, so you might want to preview it), but it is totally accessible for a smart child.

One of DS7s favorites has been "You Can count on Monsters" by Richard Schwartz... primes and factors illustrated with nearly no text. The perfect thing for a visual math kid to puzzle over for hours.

Here is Keith Devlin's review... http://www.npr.org/2011/01/22/133118069/math-isnt-so-scary-with-help-from-these-monsters

Updated up through this point. Thanks for everyone's suggestions!

New suggestion: the Poppy series, by Avi. They have some sad bits and some odd dialect, but there are a number and DS loved them.

I need some new suggestions for DS6...help!

Galaxy's Most Wanted by John Kloepfer

A group of smart kids attending STEM camp summon alien life to Earth and then have to put their "planet-sized" brains together to stop an alien invasion.

DS7 is loving it.

The City of Ember series by Jeanna DuPrau (4 books, sci-fy)
The Lemonade War series by Jacqueline Davies

Updated through this point.