The Holocaust (with a reported 6 million Jews killed) was kept quiet for years from other Jews and the German masses. If the death of 6 million people can be kept quiet for years in an era of radio and newspapers, why not in a primitive era of no media.
You're kidding, right?
I mean, you really have to be kidding!
Nobody was unaware that the Jews were being systematically rounded up and shipped away. Nobody.
What people were unaware of was exactly what was happening after that, because the Nazis were very careful to place the concentration camps away from large population centres. The only witnesses were either Nazi guards, who weren't going to tell anyone about what was going on, or the prisoners themselves, who couldn't leave to be able to tell anyone else. As for the secret being kept for years, the exterminations began in 1941, were stepped up in 1942, as a result of the "final solution", and ended in 1945 when the camps were liberated. The secret was (mostly, see later) kept during that time because there were no witnesses to the exterminations able to come forward. As soon as the camps were liberated news began to come out and was broadcast around the world. Here's an internal directive from the BBC about the holocaust,
dated 19th April 1945. There are also links on that page to audio file of the news about concentration camps being broadcast just days after their liberation.
Of course, the Polish resistance knew about the camps, as did the UK and US governments, although they didn't make the information widely available, presumably because they couldn't corroborate the stories.
As for "other Jews", whilst they didn't know
for certain that the holocaust was happening until the liberation of the camps began, very few had any illusions about what the Nazis wanted, and what they were capable of. My grandmother's cousin was living in the UK during the war, her immediate family had been unable to get out of Germany. Everyone in the family knew that they were extremely unlikely to ever see them again.
Hardly a secret kept for years.
But the worst thing about this post (and seriously it takes a lot to be worse than your factual errors, and dishonest misdirection) is that you are comparing two entirely different situations. On one hand you have the removal of millions of people from their homes, on the pretext of taking them to forced labour camps (a story which was believed by most people largely because it was, in part, true), where they were quietly exterminated, leaving very few witnesses, and none who were free to go anywhere to tell people about it until after the liberation of the camps. On the other you have soldiers coming into a large town, killing all the babies, and then leaving, which certainly allowed the citizens of that town to tell other people about what had happened, within hours of it happening.
You really need to do some research before you start spouting half truths and lies on such well documented subjects.