How long does childhood last?

I was just pondering the thought, when do people change from kids to teens? I know that it is suppose to be at 13 (unless you count stupid "pre teen") but the age children have been supposeably maturing is getting lower and lower. I mean back in the day i am sure kids didn't mature and think about boys and dating and that stuff untill about 13ish. But now adays you see kids in 4 inch heels with their bras showing above their halter-tops at age 7 (saw this at the B.V.J. parade!). And so many kids run around singing songs at the top of their lungs that they think are just cute innocent little songs (candy shop for example) and shaking their asses like they see on t.v....it's horrible! but i don't know i am just getting mad and making no sense. Good day. Liz out.