This group of books (and there are more) are all written by John Himmelman (CT author) and are very good examples appropriate for k-6
A Salamander's Life
Slug's Life
A Dandelion's Life
An Earthworm's Life
A House Spider's Life
A Salamander's Life
Turtle Tide by Stephen Swinburne
Frogs by Nic Bishop
The Elephant Scientist by Caitlin O'Connell
Also: Biographical - I would use most of these for k-6 depending on the class and how you teach the book
I Could Do That! Esther Morris Gets the Vote by Linda Arms White
The Story of Charles Atlas: Strong Man by Meghan McCarthy
Night Flight by Robert Burleigh
Keep On! by Deborah Hopkinson
Pop! by Meghan McCarthy
The Camping Trip That Changed America by Barbara Rosenstock
Queen of the Falls by Chris Van Allsburg
The Dinosaurs of Waterhouse Hawkins by Barbara Kerley
When Marion Sang by Pam Munoz Ryan
Me... Jane by Patrick McDonnell
The Story of Ruby Bridges by Robert Cole
Wilma by
One Tiny Turtle by Nicola Davies
Surprising Sharks by Nicola Davies
14 Cows for America by Carmen Agra Deedy
Henry's Freedom Box by Ellen Levine
Balloons Over Broadway by Melissa Sweet
Chapter book- Claudette Colvin by Philip Hoose- grade 5 and up- Have not read it, but it sound good.
Marching For Freedom by Elizabeth Partridge --80 pages-grades 5 and up
Bad News for Outlaw by Vaunda Nelson - 40 pages - Grades 3 and up