Hi Dana,
Here are some more, these are picture books:
Are You a Butterfly? (Judy Allen/Tudor Humphries) This is a series there is also Ant, Bee, Dragonfly, Grasshopper, Ladybug, Snail, Spider . My 4 year old LOVES these! The are shorter and give quite a bit of info about each insect.
Monarch and Milkweed (Helen Frost/Leonid Gore) Tracks the life cycle of the milkweed plant and monarch butterfly
A Tree Is Nice (Janice May Udry/Marc Simont) trees
Rain (Peter Speir) No words, but delightful illustrations!
Rabbits & Raindrops (Jim Arnosky) Jim Arnosky has ALL KINDS of great books, we just happen to have the rabbits & raindrops one. He’s a fabulous nature author/illustrator to look up by name.
Owl Moon (Jane Yolen/John Schoenherr) great horned owls
The Wheel on the Chimney (Maraget Wise Brown/Tibor Gergely) storks migrating
The Big Snow (Berta & Elmer Hader) this one is longer
The Happy Day (Ruth Krauss/Marc Simont) spring arriving in the forest
And then It’s Spring (Julie Fogliano) boy planting garden
Not nature, but since you have a 4 year old, Over in the Meadow (illustrated by Ezra Jack Keats)
The Storm Book (Charlotte Zolotw) this one is also longer
not nature per say, but seasons The Year at Maple Hill Farm (Alice & Martin Provenson) follows farm animals thru the year. Also longer, but both my dc loved it.
The Among the People series is by Clara Dillingham Pierson and you should be able to find them free online. Have fun with Thorton Burgess!