On a recent Wednesday morning in Williamsburg, Brooklyn, parents and children met up in McCarren Park with all manner of wheels: electric cargo bikes, scooters, tricycles, classic cruisers. By 7:30 a.m., about 30 people were ready to roll.

Around the same time, a similar scene was unfolding in Brownsville, Brooklyn, where cyclists wearing high-visibility vests gathered at the corner of Bergen Street and Rockaway Avenue. As “Happy” by Pharrell Williams played on a speaker, the pack started to roll west, toward Boerum Hill. Along the way, other families, tracking the group’s location, joined the slow-moving peloton, also known as the “bike bus.”

The bike bus is an increasingly popular way to get to school. In the fall of 2021, the trend made headlines in Barcelona (known there as bicibús). Gradually, it made its way stateside and to the Metropolitan area. Some fans have nicknamed the movement “kidical mass,” a play on a cycling event where groups spontaneously take over the streets.

When Drury Thorp, a teacher at Watchung Elementary School in Montclair, N.J., read an article about a “bike bus” in Portland, Ore., she reached out to a local cycling group, and they charted a route.

“I had been riding my bike every day anyway,” Ms. Thorp said. “I thought, ‘How cool would it be to do that with kids?’”

How bike buses work depends on location, infrastructure and resources. In Montclair, where residents put bright red signs on their lawns proclaiming their participation, multiple routes go to seven schools. The Bergen Bike Bus in Brooklyn is a five-mile stretch that serves at least five schools. And the one at McCarren Park heads to P.S. 110, a 10-minute ride away in Greenpoint. (Coffee and pastries, donated by the P.T.A., await their arrival)

As the weather warms up, more families seem to be tagging along. The pandemic saw an uptick in parents opting to take their children to school on bicycles. And ongoing remote work habits have given many people the time to continue the practice. Research shows that children arrive at school more engaged when they walk or cycle there.

But there’s a way to go before the bike bus trend hits “kidical mass.” In 1969, nearly 50 percent of children walked or cycled to school. Now, the rate is closer to 13 percent. Growing up in Montclair, Ms. Thorp said she biked to school with friends. “I just didn’t see that anymore,” she said. “That was an impetus,” she explained, to start a bike bus.

Cai Ciaccia, a fifth grader at P.S. 110 who lives in Greenpoint, said he preferred cycling with his friends over walking or taking the bus. “This is faster, and more fun,” he said in the morning before entering the school. “My legs are a little tired, but I feel relaxed.”

Typically, parents and teachers lead the students in the bike bus, but cycling advocates often act as attachés. In Montclair, a group of older men known as the “Grey Riders” regularly join to ensure everyone’s protection. In Brooklyn, organizers from Transportation Alternatives and other safe streets groups often serve as “captains” or “cabooses” of the pack. They help stop traffic at turns, and lead groups through green lights.

Joshua Magpantay, 24, started volunteering after meeting Emily Stutts, a teacher at P.S. 372 and the coordinator of the weekly Bergen Bike Bus, at a vigil for a cyclist who was killed this winter in Gowanus, Brooklyn. Now, he plans trips around the bike bus schedule, he said. “My mom in Texas asked me to come visit, and I said sure, but I need to be back by Wednesday.”

Bike bus participants hope that its growing popularity will convince local leaders to do more on issues like speeding and congestion. “We want to show people that you can’t have safe streets for kids unless you literally have people guiding the way,” said Chris Roberti, a father who helps organize the ride to P.S. 110.

The school lost Matthew Jensen, an English teacher, to a hit-and-run two years ago. The tragedy galvanized the community to push the city to redesign McGuinness Boulevard, the high-speed thoroughfare in Greenpoint where it happened. These days, a bike bus passes through it, with a police escort.

For now, bike bus routes tend to exist in whiter and wealthier neighborhoods. When a reporter joined the Bergen route, no children participated for its first mile through Crown Heights, where cycling infrastructure is less accessible. In Montclair, families from the South End section of town, which tends to be less prosperous, were underrepresented.

“We have a pretty strong equity agenda, and we need the demographics to look different than they do today,” said Stephen Meyer, a parent and organizer in Montclair. The group is working on more outreach ahead of the next school year.

For now, families are enjoying their last rides of the academic year. Recently, as a “bus” made its way to Nishuane Elementary School, a young girl named Lillian pedaled along. Once she arrived, she let out a sigh of relief and exclaimed: “This is why I love Fridays.”