By a 5-4 vote, the high court held the suspect's age was a factor that must be taken into account in determining if the juvenile felt free to end the police questioning.
"It is beyond dispute that children will often feel bound to submit to police questioning when an adult in the same circumstances would feel free to leave," Justice Sonia Sotomayor wrote in the majority opinion.
"Seeing no reason for police officers or courts to blind themselves to that common-sense reality, we hold that a child's age properly informs" the analysis of whether the juvenile is in custody and must be told of their legal rights, she said.
The court's four staunchest conservatives dissented.
"The court's decision in this case may seem on first consideration to be modest and sensible, but in truth it is neither," Justice Samuel Alito wrote, saying the ruling was not needed to protect the rights of minors during police questioning.
That position had been argued by the Obama administration, which said clear guidelines already existed for police and courts on questioning suspects. It opposed adding age as a factor.