Unscramble for December

Solve this popular children's rhyme.


Viadhm Riadhm goh cb o kozz
Viadhm Riadhm vor o ufsoh tozz
Ozz hvs ywbu'g vcfgsg
Obr ozz hvs ywbu'b asb
Qcizrb'h dih viadhm riadhm hcushvsf ouowb.

Hint:

b = n
c = o
h = t
o = a

Have fun!