I hope Sally has joined us from the other thread; yes, searching the DT under @west brings up a few things. How clever of me to have thought of a lot already.
For fifth graders?? Well, Mrs. Samuel taught us the bowdlerized version of that back in school, and we liked it. (and Sourwood Mountain, and a lotta other good stuff. Thanks, Mrs. S., wherever you are.)
Westward expansion tends to depend on where you are standing. 200 years ago, crossing the Alleghenies made you a pioneer.
Erie Canal is a pioneer song; anything about Johnny Appleseed qualifies; "Please, Mr. Custer" if you want to stretch. The 784 secti9on of your school or public library will have folk song books, including cowboy songs (well, they should, anyway.)
Playing the midi files in class is a stroke of genius.