Here is a good one to warm up on these frosty winter mornings.  Remember to do all of the actions and move those fingers, thumbs, arms, legs and heads.  Gets very energetic at the end! 

Red and yellow and pink and green 
​purple and orange and and blue
I can sing a rainbow, sing a rainbow, sing a rainbow too
Listen with your eyes, listen with you eyes and sing everything you see
You can sing a rainbow, sing a rainbow sing along with me

It is very traditional in UK schools to have assembly in the morning, when all school children get together in a big hall, sing, listen to stories and are given any important communications.  I remember assembly time as great fun and we would often sing along to the Beatles with Mr. O'Conner the music teacher at the piano!  Here is a lovely assembly morning song to learn and to stretch to!