Who???

A group of us talking the other day about what we would do if we had a time machine.  It was inevitable that sooner or later someone would say that they would go back to when Hitler was an infant, and kill him - thus avoiding the Second World War and all its associated nastiness.  But assuming that the adult Hitler's non-existence would indeed have prevented WWII, you then have to face the paradox that, if there were no World War II, you would have no reason here in the present to go back in time and kill Hitler!