I taught school for over thirty years and taught a bunch of songs to kids and learned a bunch from kids as well.
They seemed to like:
Boodle-Am Shake,
Be Kind To Your Parents,
Carl Martin's Barnyard Dance,
Rosalee Sorrel's I'm Gonna Tell,
The Watermelon Song,
Singing In The Bathtub,
Hopalong Peter (I leaned it from the New Lost City Ramblers)
Beans In My Ears (Len Chandler)
Going To The Zoo (Tom Paxton)