Informed people had known something of Roosevelt’s difficulties since the 1920’s. His laborious walk to the podium, on crutches and on the arms of his teenaged son, to nominate Al Smith had been one of the most dramatic moments of the Democratic National Convention of 1924.
When he ran for the nomination in 1932, his disability was used against him. “We don’t want a dead man on the ticket,” said rival William Gibbs McAdoo. “It requires a man of great vigor and bodily strength to stand the physical strain of it,” said Al Smith (by then an opponent). So Roosevelt’s disability wasn’t exactly a secret, at any time.
He did, however, manage to conceal its severity. He gave the impression that he could walk a little bit, when in reality he could barely stand up. He was aided by cooperative photographers and the press, especially after he became president in an era when the office was granted greater respect than today.
So it’s not as if people were either aware of Roosevelt’s disability, or not. Many more informed people were aware of the disability, but not of its severity. Less informed people, especially those who came of age after Roosevelt became president, were barely aware of it at all.