Why are the authorities helping the McCann's and not all the kids that must go missing all over the world?

It's media coverage. If you can't attract media coverage, you're sunk. But the media wants those things that will draw attention to themselves--cute, adorable things. That's why teens get more attention than adults, children more than teens, cute children more than ugly ones, and puppies more than children. It's obscene how people come out of the woodwork throwing donations and offers of adoption when an abused animal makes the news. With the McCann case, there's also the element of mystery. Like UFOs, that keeps people riled up. And no, it isn't an ignorant question at all. Your question highlights something in human nature.