Final answer:
The U.S. Supreme Court deemed life imprisonment without parole for non-homicide juvenile offenders unconstitutional in Graham v. Florida (2010) and further addressed juvenile sentencing in Miller v. Alabama (2012).
Step-by-step explanation:
The U.S. Supreme Court announced that sentences of life imprisonment without the possibility of parole imposed on children convicted of non-homicide crimes were unconstitutional in the ruling Graham v. Florida, 560 U.S. (2010). Following that, the Court further clarified in Miller v. Alabama, 567 U.S. (2012) that such life sentences may not be mandatory for juvenile offenders. These decisions highlight the Supreme Court's involvement in ensuring the Eighth Amendment's ban on "cruel and unusual punishments" applies to juvenile sentencing, reflecting a broader concern over excessive or disproportionate punishment as explored in cases like Kennedy v. Louisiana and Roper v. Simmons.