As a former substitute teacher for Pre-K to 5th grade music classes, I always liked having age-appropriate sing-along songs handy, that students loved singing. Here are some of my favorites for Pre-K classes (for Pre-K it may be best to share just the chorus, as it helps to keep it simple to maintain their interest):
I’m a Little Teapot (The perfect length for pre-schoolers, and they like the gestures that go along with the song)
You Are My Sunshine (My mother sang the chorus from this song to me and my daughter when we were both young; the chorus is what I share in class)
It’s an Insect Not a Spider Lyrics and sample available. It is sung to the tune of Oh My Darling, Clementine. This is a great way to clarify to young children that there is a clear difference between insects and spiders.
Head, Shoulders, Knees, and Toes (This is great for getting students moving)