Try these for fun warm ups:
Sing scales and arpeggios to “ho, ho, ho”
Sing “roasting chestnuts” on a single note up and down the scale
Sing a descending scale to “dinga, dinga”
Sing “jingle, jingle” on a single note to a 5 note ascending scale
Sing “pring, pring” to a descending scale
Christmas tongue twisters:
twirling tinsel round the tree
red nosed Rudolph running round
I spy mince pies