Offers of help are pouring in for an eight-year-old Liberian girl disowned by her own family in Phoenix, Arizona, after being raped by four boys.

The girl is under the care of the Arizona Child Protective Service (CPS) because her parents said she had shamed them and they did not want her back.

Phoenix police said calls had come in from all over the US offering money, or even to adopt the young girl.

The boys, Liberian immigrants aged nine to 14, have been charged with rape.

The case has sparked outrage across the US and even drawn condemnation from Liberian president Ellen Johnson-Sirleaf, an outspoken anti-rape campaigner.

"I think that family is wrong. They should help that child who has been traumatised," Johnson-Sirleaf said. "They too need serious counselling because clearly they are doing something, something that is no longer acceptable in our society here," she added.

Media reports said the girl was lured into a shed on 16 July with promises of chewing gum by the four young boys. There, they held her down and took turns assaulting her for 10 to 15 minutes, before her screams alerted police officers nearby.

The oldest suspect, a 14-year-old, will be tried as an adult on charges of kidnapping and sexual assault, police said on Friday. He is being held in police custody until trial. The other three – aged nine, 10 and 13 – are charged as juveniles with sexual assault and kidnapping.

Police said no charges will be filed against the parents.

"They didn't abandon the child," Phoenix police sergeant Andy Hill said.

"They committed no crime. They just didn't support the child, which led to CPS coming over there."

Hill said people from eight or nine US states had called wanting to adopt the girl or donate money.

"It has been unbelievably fantastic in terms of support for the child," he said.