A simple beginner book for young children on this topic is Birds by Kevin Henkes.
As an introduction, the text deals with basic characteristics of birds. It also considers imaginative questions about them, "If birds made marks with their tail feathers when they flew, think about what the sky would look like?".
The bold acrylic paintings by Laura Dronzek are lovely and convey the simple beauty of the birds. This is an excellent read-aloud choice that provides both fact and fantasy.
Field Trip Extension Idea:
If you live in the area, make a date to visit the Louisville Nature Center.
You can visit the Bird Blind, take a hike, or try one of the preschool programs.
Here's one coming up: "Beaks and Squeaks: All About Backyard Birds"
If you're from out of town, set up a feeder in your own backyard and let your child observe the birds who come to visit you!