The activists worked their way down the crowded aisles of a Downingtown beer distributor this week, slapping cases with stickers warning against underage drinking over the July Fourth weekend, which rivals the Christmas season for dangerous bingeing.

This, however, was an anti-alcohol campaign with a twist. The teetotalers were teenagers, on a mission to persuade parents not to serve alcohol to minors at holiday parties.

Even on grown-ups, "there's peer pressure," said Taylor Root, 15, a rising sophomore at Downingtown West High School. "They want to be cool for their kids."

Called "Parents Who Host Lose the Most," the project was started by Prevention Action Alliance, formerly Drug Free Action Alliance, a national agency that has battled substance abuse for the last three decades.

In Downingtown, the local organization Communities That Care finds student volunteers to spread the word that there is nothing cool about parents who enable underage drinking. Four times a year, when partying is at a peak, eight to 10 teens spend an afternoon at a beer distributor, as well as put signs in shop windows and on tables at local restaurants.

"Prom, graduation, senior week," said Libby Egnaczyk, director of Downingtown CTC. And don't forget Christmas, with its avalanche of adult parties where youngsters can easily down a few cold ones while mingling with their elders. "Celebratory times are huge," she said.

According to Prevention Action Alliance, 29 percent of parents and teens know of parents who host parties where minors imbibe, and 25 percent of teens have attended such a gathering. Every day, 5,400 young people under age 16 have their first drink.

Everyone at school knows the families involved, and kids gravitate to those houses, said Eric Ferguson, 19, who graduated from Downingtown East High School last year.

"There is usually drinking in the basement," he said. "The parents know what is going on."

If the party gets busted, the penalties are stiff for the adults in charge: up to $2,500 for every child caught drinking in their house, and possibly a year in jail.

Egnaczyk said she knows of one family that was caught with 40 teens drinking in their house after prom. The parents were fined $2,000 per minor and had to sell their house because they couldn't afford the $80,000, she said.

Some families send out emails alerting other parents that they will be hosting parties where teens will have access to alcohol, Egnaczyk said. By signing the email, parents give permission for their children to attend.

"They say, 'If you like, we can keep the keys. The kids drop them in a basket. How safe are we?' " she said. "But what about that kid that has a fight with his girlfriend at 3 in the morning and leaves and gets into an accident? Who's responsible? People don't think."

The hosting parents believe the emails afford them legal protection, but they are still liable for anything that happens to a child who was drinking in their house, she said.

Dana Rachko, a prevention specialist in the organization's Media office, said she hears from parents who think it's safer for kids to drink in the home. They think "if they took away keys, it's going to be fine," she said. "We always say taking away the keys doesn't take away the risk."

Many parents don't realize that today's teens drink far more than did those in beer-guzzling days of yore.  "Ten to 20 years ago, binge drinking wasn't as much of a thing," Rachko said. But Generation Z, the cohort following millennials, favors hard liquor and alcohol games – "shot after shot after shot," she said.

Parents also have told Rachko that they want to "teach" their offspring to drink before they go to college, but she tells them that strategy is ill-advised, since it only builds up their tolerance.

Studies have shown that alcohol consumption by adolescents results in brain damage, possibly permanent, and impairs intellectual development. Moreover, children who drink alcohol by seventh grade are more likely to report academic problems, substance abuse, and delinquent behavior in middle and high school and to have employment problems in adulthood.

The teens at the beer distributor struggled to come up with reasons that parents serve alcohol to minors. They want their children to like them better, some guessed.

But 16-year-old Kenneth Donahue, a rising junior at Downingtown East, had another thought as he put stickers on cases of Coors.

"Some might think their kids are mature enough," he said, "or some just don't care."