When Caitlin Miller's teachers took her to the principal's office, she did not understand why.

The five-year-old US girl had been playing with her best friends during recess in the playground at her North Carolina school, just like any other day.

She pretended her two friends were a king and queen, and that she was in charge of protecting the kingdom. "I was the guard," Caitlin told WTVD.

REUTERS, FACEBOOK Caitlin Miller used a stick to "defend the kingdom" during playtime at recess. Her school wasn't having it.

Noticing a stick shaped like a gun on the ground, Caitlin picked it up and pretended to shoot intruders entering the kingdom.

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But by playing with this stick, her school administrators said, Caitlin was violating school policies.

FACEBOOK The "stick gun" in question.

The child was suspended for one day for "turning a stick into a gun and threatening to shoot and kill other students", the elementary school's assistant principal wrote in a note to Caitlin's parents.

School officials even attached a picture of the stick she was using, which Caitlin's mother posted to Facebook.

"One minute she's playing with her friends and the next her teachers are dragging her to the principal's office," her mother, Brandy Miller, told WTVD. "She's confused. Nobody explained anything to her."

REUTERS Caitlin's mum Brandy Miller wants the school to apologise for sending her home.

Caitlin didn't understand what a suspension was, or why it was happening to her, her mother wrote on Facebook.

Miller struggled to explain to her child that it was wrong to play certain games at recess, because she felt a child her age should be allowed to play make-believe games. She didn't want to have to discuss school shootings with her daughter, or tell her that she's not "allowed to play like that at school because people do bad things to kids your age".

She told her daughter, "you can't say you're going to shoot and kill people". And Caitlin looked at her, confused, saying "I never said that?" her mother wrote on Facebook.

In a statement to WTVD, the Hoke County Schools district said it "will not tolerate assaults, threats or harassment from any student".

"Any student engaging in such behaviour will be removed from the classroom or school environment for as long as is necessary to provide a safe and orderly environment for learning," the school system said.

It added its policy "prohibits retaliatory isolation of individual students, and the system's first priority is to provide every available opportunity for student success".

Caitlin returned to school Tuesday after her one-day suspension, and felt alienated by her friends and teachers as a result of the punishment, her mother said.

"She feels like all the teachers hate her," Miller wrote. "I can't imagine being 5 and feeling that way."

The mother said she felt Caitlin's game at recess was "blown way out of proportion".

"Don't they still make Nerf guns and water guns that kids shoot each other with?" Miller wrote on Facebook. "Don't kids still play paintball and laser tag? I can see a suspension for an older kid who knows better and who is actually threatening other kids."

Friends and family members expressed outrage at the suspension on Facebook. Some pointed out that Caitlin's father serves in the Army, so she has grown up understanding the role that guns play.

Miller wants the school to right the wrong.

"I just want them to apologise to her and tell her it's okay," she told WTVD. "You can be five and have an imagination."