Then we talked about playing a song faster and louder (crescendo, accellerando) and did Jingle Bells getting faster and louder with each chorus.
Next we talked about slower and quieter and did Away in a Manger as a lullaby until we thought the baby had gone to sleep. We'd ask, "Would you sing this real loud to get a baby to go to sleep?"
Then we discussed slowing a song and did We Wish You a Merry Christmas and we did a nice slow ending.
You can do all the above as a soloist, too. But the next couple songs require a 2d person.
We discussed Call and Response and did the Raffi song Must Be Santa with one person doing the lead (call) and the others doing the response. The kids generally sang along with both sides which was okay.
We discussed harmony--doing high and low singing at the same time--and did Silent Night, ending on a quiet tune so the kids wouldn't be so wound up.
Other ideas
At public school, I stay away from actual Christian songs for singing,
but will often play an instrumental of one. Easy ones that I like
are:
Silent Night, Away in a Manger,
and
Angels We Have Heard on High