Hi Mary!It �s so useful to sing a song like warming up. 
My favourite one is this (you can sing it with an easy melody):
"Good morning to you, good morning to you
everybody is quiet and paying attention
this is the way to start a new day"
All the class should performance it doing a "be quiet" sign (for example, putting your finger in the mouth and raising the other hand). 
Each time a student talk, you do that sign and all the class imitate you. This is so good for young learners. 
Good luck!
Kisses.