Seems to me that what you want is to involve the children and make the learning fun. I would go for just the 12 days of Christmas and make a big production of it.
Sheet music:
kididdles.com/pdf/twelvedaysofchristmassheetmusic.pdf
 
Write the elements of the 12 days (Partridge in a Pear Tree, Two turtle doves etc) on cards. Forget the guitar. Just sing and hold up the card so that the kids can join in. Start slowly and then speed up as you have more of the 12 days to sing. Then give the cards to twelve of the children and have them try and hold them up at the right time (perhaps teacher might tap each one gently on the shoulder to remind them!). Everyone dissolves into giggles as teacher dashes back and forth along the line of kids with cards and great fun is had by all - and they learnt some not very easy English words! Afterwards you could also get the children to draw on cards what each of the 12 days actually look like - give a prize to the best.

craigb
I think December 22nd is the best day.
('Cause it's my birthday!) 

Also typically the second-shortest day of the year.
 
Here in the US we have something called President's Day, which celebrates the birthdays of two of our favorite presidents, although it almost never falls on either of their actual birthdates. It's always on a Monday, to make sure union workers get a three-day weekend out of it.
 
That practice has inspired me to personally move Christmas to December 26th. There are many benefits: Christmas lights are half-price and Christmas trees are free. Everything's on sale, restaurants are open, and the bell-ringers have gone home.
 
Feel free to join me in celebrating the 5th of July next summer.