A group of 17 boys, aged as young as 14 and mostly Indigenous, were shifted last month from Banksia Hill detention centre to a new unit at nearby Casuarina prison.
Between their arrival on July 20 and August 8, there were three attempted suicides and 13 minor self-harm attempts at the facility known as Unit 18.
The figures were provided by Western Australia's government in parliament on Thursday in response to a question from Greens upper house MP Brad Pettitt.
Government MP Matthew Swinbourn, representing the corrective services minister in the Legislative Council, confirmed four children had been involved in a self-harm attempt last week which resulted in one boy being hospitalised.
The boy returned from hospital the same day with no further medical intervention required and was provided with mental health support, he said.
Officials have said they were left with no choice but to transfer the boys to Unit 18 because they had been destroying property, escaping from their cells, assaulting staff and harming themselves.
They have promised the detainees will be kept away from adult prisoners in safe and secure units while repair works are completed at Banksia Hill.
The number of self-harm and attempted suicide incidents at Banksia Hill has spiked over the past three years.
Megan Krakouer, from the National Suicide Prevention and Trauma Recovery Project, said there was an "ongoing crisis" in youth detention.
"The self-harms will continue this year, next year and the year after unless we radically reform the system," she said on Friday.
Corrective Services Minister Bill Johnston this week said the remaining detainees at Banksia Hill were now in a "much better" environment.
"It was not functioning to have these young offenders causing violence at Banksia Hill, so that the other kids ... were not getting the services they need because the facility was constantly going into lockdown," he told reporters.
He said the boys at Unit 18 had access to education, cultural, medical and psychological services and secure recreation facilities.
They were being regularly assessed and would be returned to Banksia Hill once it was deemed safe for them to do so, he said.
An independent inspector this year found some boys at Banksia Hill were spending as little as one hour a day outside their cells, in violation of their human rights.
About 600 past and present detainees have signed up for a planned class action against the state government.
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