I use the Wee Sing series. A lot of the kids have these tape/book sets and have heard the tunes over and over, and the book has easy arrangements you can use and they can learn too, if there is an autoharp available. Some are call/response or action songs.

Spirituals, being call/response, work well too. See the African American Spirituals Permathread for a list of what's here.

~Susan