I got a lot of my ideas from preschoolalphabet.blogspot.com
B is for Bat
Read about bats and look at pictures of bats on the internet.
Go on a bat hunt. Hide bat cut outs with googly eyes and a fact about bats written on them in white around the house like these. Give your preschooler a flashlight and let them find the hidden bats. When they find them, read the information about bats together.
Love this idea: http://www.readingconfetti.com/2011/10/handprint-bats.html
B is for Butterfly
We also made a large flower cutout with a hole in the middle and put it over a cup with juice. He put a straw through the whole to sip the "nectar." We also made these butterfly cut outs and listened to the song found here.
B is for Baa Baa Black Sheep
Lots of fun from preschoolalphabet. My son liked doing all of these.
B is for Bear
Again, lots of great ideas from preschoolalphabet.
And I love this idea to add sound effects to "We're Going on a Bear Hunt."
B is for Books
Go on a Book Scavenger Hunt (idea from here.)