The following script is from "Saving the Children" which aired on April 27, 2014. Bob Simon is the correspondent. Harry Radliffe and Vanessa Fica, producers.

Now, an extraordinary story from the Second World War -- a humanitarian story that didn't come to light for decades. It concerns a young Londoner named Nicholas Winton who went to Prague, and ended up saving the lives of 669 children, mostly Jews, from almost certain death. His story begins at the end of 1938, with Europe on the brink of war. In Germany, violence against Jews was escalating and the infamous Munich Agreement paved the way for Hitler's armies to march unopposed into Czechoslovakia.

In London, Nicholas Winton had been following events and knew that refugees fleeing the Nazis were in dire straits. He went to Czechoslovakia to see if there was anything he could do to help. What's strange is that for almost 50 years, he hardly told anyone about what he had accomplished and for 50 years, the children knew nothing about who had saved them or how.

We begin on October 1st, 1938. Nazi troops marched into the Sudetenland, the German-speaking region of Czechoslovakia. Prague, the Czech capital was flooded with desperate people, trying to escape. A fortunate few were able to send their children abroad. These parents, mostly Czech Jews, sensed war was coming and wanted to get their children out. By chance, a cameraman filmed a man holding a boy, a 29-year-old Londoner. His name: Nicholas Winton.

Nicholas Winton: All I knew was that the people that I met couldn't get out. And they were looking of ways of at least getting their children out.

Nicholas Winton is one of the few people who can bear witness to those days because he's 104 years old. He told us he went to Prague to see if he might be able to save some people.

Bob Simon: What made you think you could do it?

Nicholas Winton: I work on the motto that if something's not impossible, there must be a way of doing it.

Back in London, Winton was a successful stockbroker -- living the good life, with a passion for sports. But he was deeply concerned about news reports from Czechoslovakia, of "German persecution."

Nicholas Winton: I went out into the camps where the people who had been displaced were put. And it was winter. And it was cold.

Emigration wasn't an option. The world's doors were closed to refugees. Conditions in the camps were brutal for the 150,000 people trapped there, especially for the children. And no one focused on them until Nicholas Winton.

"I work on the motto that if something's not impossible, there must be a way of doing it."



But what did he do? We went to Jerusalem, to Yad Vashem, Israel's memorial to the victims of the Holocaust, and asked Dr. David Silberklang, a senior historian there.

David Silberklang: Winton went set up shop in a hotel in the center of the old city in Prague, and began looking into, "How can I organize getting some of these refugees, particularly the children, out of here?"

Bob Simon: What kind of experience did he have to qualify him for this immense bureaucratic task?

David Silberklang: None!

Winton set up a small organization with one aim: to get as many kids out, as fast as possible.

David Silberklang: People started coming to him in increasing numbers. He didn't have time in the day to meet them all. He'd work till 2:00 in the morning; get up early in the morning to meet the next people as more and more were coming saying, "Take my child. Take my child."

By the time he returned to London, he had a list of hundreds of children and set out to convince British authorities to take him seriously. He did it by taking stationary from an established refugee organization, adding "Children's Section," and making himself chairman.

Nicholas Winton: So that eventually they had to adopt me.

Bob Simon: So, in fact, you managed to do what you did through a little deception, a little smoke and mirrors?

Nicholas Winton: Yes, to a certain extent, yes.

Bob Simon: It required quite a bit of ingenuity.

Nicholas Winton: No, it just required a printing press to get the notepaper printed.

The "Children's Section" operated from a tiny office in central London. Winton's mother was in charge. The staff were all volunteers. During the day, Winton worked as a stockbroker. Evenings, he wrestled with the British bureaucracy.

Bob Simon: Did you approach any other countries to take some of the children?

Nicholas Winton: The Americans. But the Americans wouldn't take any, which was a pity. We could've got a lot more out.

Winton had written President Roosevelt, asking the U.S. to take in more children. A minor official at the U.S. Embassy in London wrote back -- the U.S. was "unable" to help. Britain agreed to accept the children, but only if Winton found families willing to take them in. So he circulated the children's pictures to advertise them. But even after a family chose a child, British authorities were slow in issuing travel documents. So Winton started having them forged. He also spread some money around.

Nicholas Winton: Took a bit of blackmail on my part.

Bob Simon: You were indulging in blackmail and forgery to get the children out?

Nicholas Winton: I've never heard it put like that before.

Bob Simon: But you seem to be enjoying it.

Nicholas Winton: It worked. That's the main thing.

The first 20 children left Prague on March 14, 1939.

The next day, German troops occupied Prague and the rest of Czechoslovakia. Hitler rode through the streets triumphant. Hugo Meisl was 10 years old.

Bob Simon: Do you remember the Germans coming into Czechoslovakia?

Hugo Meisl: Not only do I remember, I personally saw Hitler standing up in the car. And the children were expected to say, "Heil Hitler," and so forth. I remember as if it was yesterday.

It wasn't long before violence against Jews, property confiscations and forced labor that began in the Sudetenland spread throughout Czechoslovakia. But the Nazis allowed Winton's trains to leave - in keeping with their policy to "cleanse" Europe of Jews. Hugo Meisl's parents decided it was time to put him and his brother on one of the trains.

To learn more about the Kindertransports, Kinder and their descendants today, please see www.kindertransport.org

Hugo Meisl: I remember that they told us that we were going to England maybe two or three months. It would be a holiday for us. And that they would join us very shortly thereafter--

Bob Simon: And you believed them.

Hugo Meisl: Absolutely.

Bob Simon: Were your parents emotional when they said goodbye to you?

Hugo Meisl: No, I re-- I-- I-- I've asked myself that question many times. How my parents had the strength (chokes up), I'm sorry. It never occurred to me that what they were saying to us was not true. In other words, that they realized that they would not be joining us within a short period of time.

Over the spring and summer of 1939, seven trains carried over 600 children through the heart of Nazi Germany to Holland, where they took a ferry to the English coast. From there, they caught a train to London.

An eighth train -- carrying 250 more -- was scheduled to leave Prague on September 1st. But that's the day the war began.

Nicholas Winton: They were all at the station. Even on the train, waiting to go, and war was declared. So the train never left. Never heard really what happened to all those children.

Bob Simon: But there's reason to suspect that not many of them survived?

Nicholas Winton: I think that's true. Yes.

Two years after that last train, the Nazis began implementing the "Final Solution" their plan to slaughter all the Jews of Europe. Czech Jews were rounded up and shipped to Theresienstadt, an old military garrison town about an hour north of Prague --- their first stop on the road to annihilation.

These tracks were the exit from Theresienstadt. The only exit. The tracks led east. The trains were called Polish Transports. Destination: Auschwitz. Some 90,000 people took that one-way ride. Among them almost all the children Sir Nicholas wasn't able to get out in time, their parents and the parents of the children already in England.

Bob Simon: After the war you went back to Czechoslovakia... Was there one instant where you accepted the fact that your parents were dead?

Hugo Meisl: For three years we used to visit when trains came from Siberia, especially when the Communists moved in in 1948, a lot of people started coming back from Siberia. So I would go to a station-- hoping. And films were being shown of people walking in concentration camps, Auschwitz and so forth, there were so many shots being taken by the Germans and-- and so forth-- never stopped looking.

The name of every Czech Jew murdered in the Holocaust is painted on the walls of Prague's Pinkas Synagogue. Over 77,300 names, including Arnoshtka and Pavel Meisl -- Hugo's parents.

And Nicholas Winton? During the war he volunteered for an ambulance unit for the Red Cross, then trained pilots for the Royal Air Force. He got married, raised a family, earned a comfortable living. For 50 years, he told hardly anyone what he had done.

Bob Simon: A question which I know intrigues everyone who hears your story, is why did you keep it secret for so long?

Nicholas Winton: I didn't really keep it secret, I just didn't talk about it.

Bob Simon: All this this time you're in England and you go back to Czechoslovakia. Then you go to Israel. You still had no idea how your departure from Czechoslovakia had been organized?

Hugo Meisl: Absolutely no idea.

Bob Simon: And you learned that by seeing it on television?

Hugo Meisl: That's right.

In 1988, the BBC learned about Winton's story and invited him to be part of a program. He had no idea, that the people sitting around him were people he had saved.

Ester Rantzen: Can I ask, is there anyone in our audience tonight who owes their life to Nicholas Winton? If so, could you stand up please? Mr. Winton would you like to turn around. On behalf of all of them, thank you very much indeed.

Nicholas Winton: I suppose it was the most emotional moment of my life, suddenly being confronted with all these children who weren't by any means children anymore.

Bob Simon: No, they weren't. And for the first time, they looked at you and knew that you were the reason that they were alive.

Nicholas Winton: Yeah. True.

Lady Milena: I wore this around my neck. And this is the actual pass that we were given to come to England. And I am another of the children that you saved.

Lady Milena Grenfell-Baines describes Winton as one of the most modest people she has ever met.

Bob Simon: Why do you think he didn't say anything for 50 years?

Lady Milena: I think it's in his nature. He really felt that he'd done all he could, and having got those children settled he felt, "Been there, done that, my job's done I've got other things to do."

"Other things." For the last 50 years, Winton's been helping mentally handicapped people and building homes for the elderly.

Nicholas Winton: We've just opened our second old people's home, and it's full. And it's doing very well. And there are plenty of old people like me to go in.

Bob Simon: Yes, but you're not there. You're at home.

Nicholas Winton: Oh, I'd hate to go into one of my own homes. Don't print that.

In 2003, Winton was knighted - and became Sir Nicholas Winton. In the Czech Republic, he's become a national hero. And he was celebrated in a documentary called "Nicky's Family," but he isn't really comfortable with all the adulation.

Nicholas Winton: I'm not interested in the past. I think there's too much emphasis nowadays on the past and what has happened. And nobody is concentrated on the present and the future.

In 1939, Nicholas Winton used a two week vacation to go to Prague and ended up saving the lives of 669 children. In the decades since, of course, the children had children, who then had children and so on...and the numbers multiplied.

Bob Simon: If you wanna summarize it in one sentence: Guy takes a two week vacation...

Lady Milena: -- and ends up with 15,000 children?

Bob Simon: It's a pretty good story.

Lady Milena: It's a great story.

Nicholas Winton: They've got children and grandchildren and great grandchildren.

Bob Simon: And none of them would be here if it hadn't been for Sir Nick.

Nicholas Winton: That's right. Yeah. Yeah. Terrible responsibility, isn't it?