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 3rd, 4th and 5th grade classes (These can also be used for 6th grade outdoor school camp songs, or brain breaks in the classroom):
Hokey Pokey (Older grades do better with added dance routines, or other movements)
My Name is Joe (a.k.a. Button Factory) (video example)
Chicken Dance