I believe the answer is:
Minors require special legal protections.
They are deemed to have no yet fully developed in term of mentality. Because of this, they punishment that given to minors tend to be more lenient compared to adults even if it's for the same crime.
He was in custody because he concluded that he was under arrest.
From this fact, justice kennedy concluded that the law enforcement has violate his miranda right.
Parents normally make the peers appear nicer than they normally are.
When, in the course of human events, it becomes necessary for one people to dissolve the political bonds which have connected them with another, and to assume among the powers of the earth the separate and equal station to which the laws of nature and of nature's God entitle them, a decent respect to the opinions of mankind requires that they should declare the causes which impel them to separation.
