Why youngsters in US have less respect to older people?

Pardon my english. But seriously, I lived in this country for almost 2 years but I find youngsters are act disrespectful a lot, not all but most of them. I saw this 13 or 15 something teenagers at Universal Studios and behaving disrespectful to this 30 something woman and her child, just because these kids are more than one doesn't mean that they can act disrespectful to older person, especially a mother!