A photographic memory has been shown to be very common amongst small children. I seems they hold a photographic image of their experiences until they can understand/deal with them. Once they start intergrating their experiences into their life their memory becomes more fluid and less photographic.
The reason we don't have a photographic (eidetic) memory as we get older is that we keep adding/linking to our existing memories to build our understanding. Our memories are excellent we just used them to build up our information banks.
Alex
