The family of an 11-year-old Aboriginal boy who suffered two black eyes and a broken cheekbone in an incident at Brisbane Youth Detention Centre claim he was “bashed” and have called for the guards involved to be stood down.

The boy, who cannot be named for legal reasons, was injured in an incident at the centre on 15 December. He told his mother during a phone call that night that he had been restrained by up to three guards, made to fall to the ground, and then slammed into the wall. But when his mother went to visit two days later she was told that guards slipped on water and fell on her son.

The incident happened soon after 3pm, when the centre was in lockdown. According to the boy, who spoke to his mother on the phone at 6pm that night, guards arrived at his cell because he had put toilet paper over the security camera before using the toilet and had forgotten to remove it.

“He said they held him, grabbed his arms to restrain him, but they were holding him too tight so he was moving around a bit,” his mother told Guardian Australia.

“And when he did that they pulled his legs out from under him and he fell on his face. He said that one of them had his legs and one had his arms, and then one of them pulled his hair and slammed his face into the wall.”

That alleged altercation happened on a Tuesday. That Thursday, when his mother travelled 207km from Dalby to visit him, she was allegedly told several different accounts by detention centre staff.

His injuries, documented in a photo taken by a nurse at the detention centre and seen by Guardian Australia, had by then developed into two large black eyes and a puffy, bruised jawline. He already had a broken hand, sustained before he was remanded in custody. His mother said she felt “sick to her stomach” when she saw his injuries.

“They said he left the smoke alarm sprinkler system on and he slipped on his face,” she said. “Another [explanation] was that they were restraining him and the guards slipped on water and fell on [him]. One other was that they said that he flooded his unit and that’s how he fell.”

The boy was seen by a nurse on the day of the incident but not seen by a doctor until the Friday, when he was allegedly taken in handcuffs to Ipswich hospital.

A spokeswoman for the Department of Justice and Attorney-General confirmed in a statement to Guardian Australia that the boy had been injured in an incident at the detention centre, and said that incident was being investigated.

However, the department did not address questions about whether any guards had been disciplined over the incident, saying “as the investigation is ongoing no further comments can be provided”.

“It is understood that on 15 December the young person sustained injuries to his face,” the department said.

Asked why he did not see a doctor until three days later, the department said in the statement: “the young person received immediate medical attention and has been provided ongoing support and monitoring. His family was advised and are in contact with the department about the progress of the investigation.

“As is standard procedure, the matter has been referred to the department’s ethical standards unit and the Queensland Police Service.”

The boy was remanded in custody in October on a string of offences, including breaching bail. It was his second stint in a youth detention centre – the first, earlier in 2015, was when he was 10-years-old, the youngest age a child can be detained in Australia. He lost his stepfather and two younger siblings in a car crash in 2011, when he was six.

An Amnesty International report released in 2015 found that Indigenous children in Queensland were 24 times more likely to have spent time in custody than non-Indigenous children. That’s slightly below the national average – Indigenous children nationwide are 26 times more likely to have spent time in custody – but the rate is increasing.

Just 7.5% of children aged 10 to 17 in Queensland identify as Indigenous, but Indigenous children make up 65% of the youth detention population.

The boy was granted bail a week after the incident and is in foster care. His mother, whom he sees three days a week, said he was having nightmares and was “shaken” when asked to talk about it.

“It hurts. It makes you sad, that that should happen. It makes me cry, the things they have done,” she said.

The boy’s father, who is estranged from his mother, said he wanted action taken over the incident.

“I want the guards stood down, I want them charged, I want them prosecuted for what they did to my son,” he told Guardian Australia.

“If this was an Aboriginal man who done this to a white child, a non-Indigenous child, bloody hell he would be in jail straight away.

“I don’t want this happening to any other children while they’re in custody.”