One of my co-workers once detailed how he thought the progression went. His version details the children getting smarter and asking questions, and in order to answer them, the story becomes larger than life.
There was a rock that crashed somewhere between Australia and Madagaskar that caused a Tsunami, but it wasn't the only thing. When the polar caps melted causing the ocean levels to raise, what we now know as the Black Sea and Persian Gulf flooded. The melting of the caps and the asteroid were thounds of years apart though. But with both events in the past, and thier inability to note the passing of time beyond a generation, it just got all rolled up into one incident.