That first-name basis reflected Mr. Sanders’s views on child development. The month Levi was born, The Vermont Freeman published a letter by Mr. Sanders lamenting the state of schooling and asserting that “many young parents are beginning to think, come what may, that it is better for their children not to go to school at all than to attend a normal type establishment.” In other writings, he championed at-home childbirth and lamented infants being “bottle fed on assembly line schedules by assembly line doctors.”

Those ideas on home schooling and home birth later became more popular. Some of his other ideas have yet to catch on.

In December 1969, he published in The Freeman “Cancer, Disease and Society,” an article based on the work of the Austrian psychologist Wilhelm Reich, exploring whether sexual repression and the stifling of children contributed to cancer.

The “manner in which you bring up your daughter with regard to sexual attitudes may very well determine whether or not she will develop breast cancer, among other things,” he wrote. He added that it was important for boys to rebel in school because if they bottled up their emotions, “30 years later, a doctor tells him that he has cancer.”

Mr. Sanders also thought children should be allowed to vote once they reached puberty. A political ally, Peter Diamondstone, who thought the voting age should be abolished altogether, recalled asking Mr. Sanders: “So every time you want to have a kid vote they have to go get a physical?”

But when it came to his own son, Mr. Sanders was more traditional.

Mr. Sanders gave clear boundaries to Levi, with whom he could occasionally be “overbearing,” according to Nancy Barnett, a friend. She recalled one day when Mr. Sanders, a former cross-country star, ran laps with Levi around the high school track until the 9-year-old stopped with exhaustion.

“Bernie was adamant,” she recalled. “‘You started your race — now you’ve got to finish your race.’”

Mr. Sanders, as his campaigning has shown, is nothing if not perseverant.