I have a short mantra where the child can select a word to place in the middle of the chant.
clapping hands while chanting the children sing two oms while clapping to the right, two oms clapping to the left and three oms clapping down the middle with hands placed high, middle and low. Once the pattern is familiar we begin to add words.
Shiva om shiva om, om om om
Shanti om, shanti om, om, om, om.
It becomes fun when the children in the class begin shouting out each other's names and their favorite animals and my personal favorite "almost om"