Whatever your opinion of Richard Dawkins, it's difficult to deny that he has a gift for explaining extremely complex and unimaginable scientific processes in such a way that a child could understand. Some of his thought experiments, such as his wonderful 'hairpin turn' thought experiment in 'The Greatest Show on Earth', are compelling for their ability to provoke an 'aha!' moment in young children, and adults who may not have had the good fortune to be taught evolution, or to be taught it well, in school.
In the below video, from his appearance at The New Yorker Festival, Dawkins walks us through one of the thought experiments in his book for all ages, 'The Magic of Reality.' Through such experiments, children can begin to grasp the immensity of time required for evolutionary change as well as the fact that no particular living thing is ever the first of its kind.