Over the years, Caroline Kennedy sometimes wondered about a third grader who wrote to her father, President Kennedy, worried that Russian bomb tests at the North Pole would kill Santa Claus.

Kennedy finally got to meet her during a segment of ABC's "Good Morning America" that aired Monday about Kennedy's recent best-selling book, "A Family Christmas," which includes the letter from an 8-year-old Michelle Rochon.

That girl, now Michelle Rochon Phillips, recounted what prompted her to write the October 1961 letter. She said she sat down to write the letter after hearing her parents talking at the dinner table about nuclear testing at the North Pole.

"I thought well, Santa Claus," she said, according to a transcript of the interview. "And so I ran, sat down at the footstool and wrote the letter."

Then a Marine City, Mich., third-grader, she wrote: "Please stop the Russians from bombing the North Pole because they will kill Santa Claus."

The president wrote back, and closed his note by saying, "You must not worry about Santa Claus, I talked with him yesterday and he is fine." He added, "He will be making his rounds this Christmas."

Caroline Kennedy said that for her father, as one of nine siblings, "Christmas was huge" and he appreciated the girl's fears. She said the letters capture how the anxiety of the Cold War and nuclear testing permeated everyday life.

"There's just so much about Christmas, and I think the history of Christmas and how it intersects with American history, George Washington, all the way up to President Kennedy," she said. "I think this is kind of the human side of Christmas, and how it's kind of become also a patriotic holiday and it's all wrapped up together."

Phillips, of Pensacola, Fla., told ABC's Claire Shipman that she wasn't trying to make a statement about nuclear testing when she wrote the letter.

"I was just worried about Santa Claus," Phillips said. "Worried about my Christmas."