Toy Brother, by William Steg. This fictional story is witty, tongue-in-cheek with keen insights into the never changing state of being human.Steg is one of my all time favorite children's authors for many reasons, including that he didn't under-estimate the intelligence of his readers.I'm predicting that both you and your children will enjoy this book and possibly all of Steg's work.
Have you heard of the series starting with the 1st book:
The Alchemist: The Secrets of the Immortal Nicholas Flamel
It is fiction, and probably geared toward middle school, but could be read by some 4th and 5th graders.
I read the whole series and really enjoyed the mix of actual history within a fictional story.
Here is the Amazon description:
"He holds the secret that can end the world.
The truth: Nicholas Flamel was born in Paris on September 28, 1330. Nearly 700 years later, he is acknowledged as the greatest Alchemyst of his day. It is said that he discovered the secret of eternal life.
The records show that he died in 1418.
But his tomb is empty."