A teacher has broken a huge Christmas rule, leaving parents and kids alike "heartbroken".

A mother in the US has complained publicly about a substitute teacher at her daughter’s school who told children in Grade 3 that Santa and his elves aren’t real.

Speaking to Fox 8 Cleveland, Ashley Coughenour from Ohio said the ‘revelation’ came when students tried to show the substitute teacher their classroom Elf on the Shelf.

According to Coughenour’s nine-year-old daughter who was in the class, the teacher replied saying “Santa Claus isn’t real, Christmas isn’t real and Christmas elves aren’t real – it’s all made up”.

"I was angry. I was heartbroken," Coughenour told Fox. "I want to know why she felt it was okay to shatter a childhood — anybody’s childhood."

Another mother posted to Facebook about the ordeal, saying the regular teacher attempted to undo the damage but some children are still confused.

"A substitute teacher decided to take it upon herself and tell the class that Elves, Santa and Christmas in general was all a lie," ‎parent Maryjo Hays‎ posted on the public page Santa Claus Writes.

"The teacher did some damage control upon returning but there's a few kiddos that are still very sad and confused and a little unsure."

LISTEN: A mum is DONE with Elf on The Shelf. Post continues below.

The school - Sterling Morton Elementary School - received several complaints and phoned the parents to say the teacher was not permitted to work there anymore.

The school's administration also issued a statement, saying: "We agree it is not appropriate for anyone working in our schools with our young children to make comments regarding their personal beliefs about the authenticity of Santa Claus. Any such comment would be made in extremely poor taste."

What a way to begin the holidays.

READ MORE: 

• A parenting expert says you shouldn’t do this if your child asks if Santa is real.
• Is it okay to lie to your child about Santa?