Peggy Charren at a 1996 White House conference on TV programming, alongside Vice President Al Gore and Tipper Gore, left, and President Bill Clinton and First Lady Hillary Rodham Clinton. (Gerald Martineau/The Washington Post)

Peggy Charren began her unlikely career as an activist when she grew alarmed at what her young daughters were watching on television — a profusion of advertisements for sugary products and “wall-to-wall monster cartoons.”

She invited other concerned mothers to her home in Newton, Mass., and in 1968 started Action for Children’s Television (ACT), which became one of the most dogged and effective grass-roots advocacy groups in the country.

She and her organization spent decades pressuring and shaming TV networks and federal regulators. They ultimately won passage of the Children’s Television Act of 1990, which limited the amount of advertising directed at children and required broadcasters to provide time for educational programming.

“Peggy Charren was the dominant voice in America for quality television, and remained so for a generation,” then-Rep. Edward J. Markey (D-Mass.) said in 1992. “We call Peggy the conscience of the broadcasting industry.” Markey, now a U.S. senator, sponsored the Children’s Television Act as a member of the U.S. House.

For her relentless activism, Ms. Charren received a special Emmy Award, a Peabody Award and, in 1995, the Presidential Medal of Freedom, the nation’s highest civilian honor.

She died Jan. 22 at her home in Dedham, Mass., at age 86. She had complications from vascular dementia, said a daughter, Deborah Charren.

The diminutive Ms. Charren testified on Capitol Hill, became a persistent presence at the Federal Communications Commission and kept the phones ringing at TV network headquarters. One CBS executive denounced her organization as “the enemy.”

Ms. Charren was unfazed.

“You make an appointment, you get up to the 90th floor, with all the carpeting and the secretaries,” she told the New York Times magazine in 1975, “and you sit down with him — it’s almost always a man — and you say, ‘You look like a reasonable guy. Why all the lousy ­programs?’ ”

Her goal from the beginning, Ms. Charren said, wasn’t to censor shows but to improve educational offerings and restrict the barrage of advertising directed at children.

“Why can’t children’s television be more like a good children’s library, with lots of diversity,” she said in 1983, “and less like the comic-book rack in the local drugstore?”

In 1974, Ms. Charren’s organization filed a petition with the FCC to eliminate advertising to children on television. At the time, there could be as many as 32 commercials in an hour, often with messages such as this one: “My tummy wants some yummy — better give it some Super Sugar Crisp!”

Ms. Charren bolstered her argument with quotations from the pages of Advertising Age, which called for thinking of “the child as your assistant salesman. He sells, he nags, until he breaks down the sales resistance of his mother or father.”

Her group grew to include 20,000 members nationwide, but it also drew opposition from high places. During Richard M. Nixon’s presidency, ACT endured a week-long audit by the Internal Revenue Service.

Later in the 1970s, ACT formed alliances with academics, medical professionals and religious groups. Broadcasters voluntarily reduced the amount of advertising on kids’ shows, and some networks — most notably PBS — became known for their innovative educational programs.

During the Reagan administration, when broadcasting regulations were relaxed, Ms. Charren turned to Congress for action. She didn’t get everything she wanted with the Children’s Television Act — advertising to children was never outlawed — but she won enough to declare victory.

She also earned the respect of some of her former adversaries, including Squire Rushnell, the onetime head of children’s programming at ABC.

“I think Peggy Charren and ACT,” he said in 1988, “have been the most significant grass-roots influence on children’s television and on all of television. Period.”

Peggy Sundelle Walzer was born in New York City on March 9, 1928. Her father was a furrier, and her grandfather was a doctor who often cared for the indigent.

An uncle by marriage, Sidney Buchman, wrote the screenplay of “Mr. Smith Goes to Washington” (1939), about an idealistic citizen who dares to challenge authority in the halls of power.

Ms. Charren graduated from Connecticut College in 1949 and worked for a New York television station before her marriage in 1951 to Stanley Charren, an engineer and businessman. After settling near Boston, Ms. Charren ran a business that presented children’s book fairs.

Survivors include her husband, of Dedham; two daughters, Deborah Charren of Northampton, Mass., and Claudia “Sandi” Moquin of Feeding Hills, Mass.; a sister; six grandchildren; and seven ­great-grandchildren.

Even after Ms. Charren closed ACT in 1992, she continued to advocate for ways to improve television and prevent children from being exposed to adult programming.

She felt so strongly about TV, she said, because she saw it as a medium of unfulfilled promise.

“That’s why I get so mad at television,” she told The Washington Post in 1993. “It can be soooo terrific. When it’s terrific, it’s really wonderful.”