The only thing this parent got wrong is the dates. Historians seem to generally think that Hitler's regime would have collapsed if the West had stood up to:
* The militarization of the Rhineland in 1936
* The Anschluss with Austria in March 1938
* The annexation of the Sudetenland (and the rest of Czechoslovakia) in October 1938
The German army was weak in the 1930s and his generals very hesitant. Hitler's "reckless" successes gave him credibility and power.
Apparently Hitler was genuinely surprised when the west declared war after the invasion of Poland. He expected the cowardly West to roll over again.
I recommend Childers' "World War II: A Military and Social History" if you're into this kind of thing.
