Two boys, aged 13 and 14, have been convicted of the gang rape of an intoxicated 12-year-old girl in the Kimberley.

The girl visited one of the boys' homes on a quiet street in Kununurra on December 24.

The 12-year-old was so drunk she passed out.

After a discussion between themselves, both boys decided to have sex with the sleeping girl.

They later put her clothes back on and called her mother to collect her.

The incident was reported to police after she woke up.

Detective Alan Goodger says the investigation was disturbing on many levels.

"There's a number of issues police are concerned with," he said.

"We're obviously very concerned when a 12-year-old girl is subject to an offence like this because we're obviously aware of the long-term effect it can have on a juvenile.

"And we're appalled at the apparent lack of supervision of those children."

Two of the boys have been sentenced to eight and 15 months' detention.

An 11-year-old also involved in the assault has been convicted and will be sentenced in August.