Underage users

Can someone explain to me why Youtube/Facebook/MySpace/Bebo/etc allow a child of the age of 11 years old to create an account on their sites without even attempting to verify their age?

I realise it states to put in a DOB, but most of these kids put in a fake one. Why not FORCE verification on the user by way of credit card, etc. If a kid wants an account their parents require a c/card to be verified.

Don't be so sure that >>5. With all the net censorship going on around the world now and with all the cp and other nasty things that happen on this site daily all it would take is some pissed off Christian mothers screaming think of the children to the goverment and this place would be screwed!! We need age verification here STAT!!!