A millennium has changed since Jessica Viestenz attended the Warped Tour — that time strictly as a fan.

It was 1998, and Viestenz, now 38, didn’t own a cellphone to stream her experience across the Internet or to call her parents. Their last conversation was about where to pick her up.

Now a mother, Viestenz and her husband, Matt, returned to Warped at Canterbury Park on Sunday to play chaperones to their daughter and her friend.

They took refuge in the “Reverse Daycare” tent, an on-site hideout for parents, among hordes of teens tagging their bodies with paint, fist-pumping and roaring with energy as performers incited them with profanities.

The tent, which boasts a “No Kids Allowed” sign, is advertised as air-conditioned, but the 50 or so adults parked on lawn chairs fanned themselves as sweat slicked their drooping faces. Sitting was a limited luxury, too, with a 30-minute cap.

While it has been a part of Warped for 15 years, tour founder Kevin Lyman made admission to the tent free (to adults 28 years old and up) in 2013.

“I always thought it was cool to have a ‘check your parents in’ option, and then for free,” Lyman said. “It brings families together, in a way.”

A TV played movies on a table beside a stack of DVDs, including mid-1980s classics “Sixteen Candles” and “Ferris Bueller’s Day Off.” Subtitles were necessary given the din of the punk, rock and alternative music. At the rear of the tent, parents grabbed energy drinks or water for free. Games of Sudoku, word searches and scrambles were available.

In its 21st year, Warped draws a mixed bag of mostly 14-to-19-year olds, decorated with temporary and real tattoos, puffing cigarettes and standing in lines for autographs by bands whose posters they clutch in both hands like a map.

The vast field is dotted with stages of new or rising bands covering songs from past stars such as Blink-182 or singing original material.

‘It’s a generational thing’

Viestenz, who was a veteran of Ozzfest and Lollapalooza, hadn’t been to a big outdoor concert since her daughter Riona Wright was born. So, in addition to supervising her daughter, she and her husband came to Warped for some fun of their own.

“It’s not that I don’t trust her,” she said. “Well, I want to go, too. You’re experiencing that together and doing what I did.”

Wright’s concert ensemble included electric blue hair, bubble-gum pink shorts and a heather gray Nirvana T-shirt. Mom didn’t cramp her style.

“If she wasn’t here, I think I’d be more nervous,” Wright said of her first go-round at Warped.

Sipping an energy drink, Mike Birtzer planned to venture to the tour’s acoustic basement after a brief rest in the parents’ tent. Birtzer, 45, had driven from Wisconsin so his stepdaughter Sienna Martineau, 16, could see her second tour with friends.

“Last year, I found bands I liked in different areas,” he said, noting indie band Echo­smith. “There are certain styles I won’t like. It’s a generational thing.”

His dad — a fan of Elvis and the Everly Brothers — would have made a beeline for a “Reverse Daycare” tent if he were at a concert like this, said Birtzer, who listened to several bands until Sienna and her friends were ready to go.

Shree Morlock found a seat along the tent’s perimeter to sip a Bud Light and play a game on her iPad. Morlock, 43, and her family of four drove five hours from North Dakota and made a weekend out of the event — her husband and son were at the Twins game. Their daughter Serena, 16, was at Warped with two friends.

“It’s not the music I listen to, but I could see it if I was at their age,” Morlock said.

An hour before their designated meeting time, Serena barreled into the tent in her black-rimmed glasses and burgundy Vans sneakers. Urgent and bubbling with enthusiasm, she said, “I got their autograph, Mom! I met them!”

But Mom wasn’t interested in that. What she wanted to know was how her daughter was doing.

“Have you guys eaten? Have you been drinking water? What about the other girls?” she asked.

Serena hadn’t found the free water station. Instead, she came to find her mom, who gave her a $20 bill to buy water.

A few minutes later, Serena returned to the tent with water. She’d found the free-water station, and had returned her mom’s $20, passing a raft of vendors selling T-shirts, cheese curds and shaved ice.

“That’s surprising,” Morlock said with a laugh.