One of the things I've learned as a sales trainer over the yeaers is that most people already know how to sell but have forgotten they have this skill. We call it persuasion or the gift of gab or even nagging, but the fact of the matter is that we are all skilled at selling.
Its when we get to be grownups and begin to fear that word as the bane of social existence, that we get all freaked out about doing this. In fact, most people, when their stress level is taken down a notch or two are incredible effective at selling things they believe in.
That's why kids are so good at it, they believe what they are telling people about what they are selling. We have all been selling since childhood, and the world is none the worse for it. And in fact most of our greatest ideas would still be simply ideas if someone had not stood up, walked out the door of the idea factory and began selling the thought to someone else.