Amnesty International has called for the US to stop sentencing juveniles to life in prison without parole.
More than 2,500 adults are in US jails for crimes committed as a child - under current rules they will never be freed.
In its new report, Amnesty says the practice is incompatible with the basic principles of juvenile justice.
The US and Somalia are the only two countries not to have ratified a UN convention that bans life in jail without parole for under-18 year olds.
'Potential for rehabilitation'
Amnesty says offenders as young as 11 have faced such sentences in the US.
"In the USA, people under 18 years old cannot vote, buy alcohol, lottery tickets or consent to most forms of medical treatment," said Natacha Mension, of the human rights group.
"But they can be sentenced to die in prison for their actions. This needs to change."
More than half of US states have approved the use of mandatory life sentences without parole for some serious crimes, such as murder.
The US Supreme Court has already acted on some aspects of youth sentencing - and a review is underway.
In May last year it banned sentences of life without parole for minors in non-murder cases.
Earlier this month, it agreed to consider the issue in relation to homicide cases, too; a decision is not expected until next year.
Amnesty's report, This is where I'm going to be when I die, says such sentences are handed down without considering factors such as history of abuse or mental health.
"We are not excusing crimes committed by children or minimizing their consequences, but the simple reality is that these sentences ignore the special potential for rehabilitation and change that young offenders have," said Ms Mension.
Amnesty wants the US to ratify the UN Convention on the Rights of the Child, which has been in force for two decades.
It prohibits the imposition of life imprisonment without the possibility of release for any offence committed by under-18-year-olds.