A friend, a child during the anti-Communist witch-hunting days in the 1950s, remembers the incident well. His parents, radicals both, took him to a demonstration protesting the execution for treason of Julius and Ethel Rosenberg. He remembers the placards a bit and he remembers some of the speeches but what he remembers most were his exaggerated fears that what had happened to the Rosenbergs could happen to his parents.

It is a view of a public event that is somewhat unique, but it may be the only way to understand Sen. Edward M. Kennedy's decision not to be a presidential candidate. What in the end deflected him, what made him reach his decision, was not the polls and not the other candidates and not the manifest political talents of President Reagan, but a kid named Patrick, 15, his youngest son. "I need you," he said.

The words as conveyed by Kennedy intimates may not be precise, but certainly that was the message. The other two children felt the same way, but in the end it was Patrick, always Patrick, who was the most concerned. It was Patrick who every night during the 1980 campaign had to get a call from his father. It was Patrick for whom a governor would be kept waiting. It was Patrick who lived with his father and it was Patrick who in the end prevailed.

Maybe there were political or other considerations, too, maybe even the realization that 1984 could, like 1980, begin like a crusade but end as an embarrassment. There were Democrats, after all, who were telling Kennedy that he could not win -- and that the Democrats needed a winner. He was a man hobbled by Chappaquiddick, a spokesman for the party's left in a country that had in almost every recent election opted for the right.

But if the decision was, as Kennedy aides say, based mostly on Patrick you could understand. Two Kennedys had been shot to death. Patrick's fears were logical. Given the number of nuts in the world and the number of guns, someone was going to take a shot at his father.

But there was more than that. There was the divorce. Once again Patrick figured. There were the long separations a campaign entails. Once again, Patrick had to be considered. Even the other children, although they had their own concerns, argued the case for Patrick. The other night at the Kennedy house, Patrick was there. The decision had been made, but not announced. He was, someone present said, "walking on air."

For Kennedy, this was nothing new. His family has been both a blessing and a curse. He was the son of a politically-active tycoon, but he was the caboose at the end of the family train -- the youngest of nine children. Even before college he had attended 10 different schools and in just four years in the 1940s, his family moved three times. If there is ever a man who knows the damage public life can do to a family it has to be Ted Kennedy.

Maybe that explains his evident conflict, a career of triumph followed by debacle -- always one step forward and two steps back. The conflict is in his voice, the hesitation, the use of impersonal pronouns. It is a constant message of I want-I don't want.

This business of finding yourself takes time. But with Kennedy a role was thrust upon him early and he is still plagued by the mistakes he made as a young man -- the cheating at college, for instance. There are ways to say "no" while still appearing to say "yes." Kennedy was a master at that, doing it last in the disjointed interview with Roger Mudd. He said he wanted the presidency but his manner said otherwise.

But now Ted Kennedy is a kid no more and some things, although not a lot, come clearer with age. Maybe the foremost is the sense that a person is only unique to his family. Others can be candidates, others can even be president, but when a boy needs a father no one else will really do.

That's about what it came down to, the Kennedy people say. On one side there was the presidency. They say the polls looked good. But on the other side, there was a boy. If this is the way it happened then Ted Kennedy, at last, knew precisely what he wanted. The presidency could wait. The boy could not.