DES MOINES — Spend even one day at the U.S. outdoor track and field national championships, and you start to wonder who forgot to check IDs and let all these kids in. Every Olympic cycle brings a new wave of potential stars, but one year out from Tokyo 2020, the new crop seems to be particularly young and particularly gifted.

Sydney McLaughlin, 19, won two Diamond League women’s 400-meter hurdles crowns this season. Rai Benjamin, who turns 22 on Saturday, is one of the world’s best at the men’s 400-meter hurdles. Michael Norman, 21, wants to break the world record in the men’s 400 meters. ­Sha’Carri Richardson, 19, just turned pro after breaking the NCAA women’s record with a 10.75-second 100 meters as a freshman at LSU.

The most precocious of all of the athletes here this weekend has yet to attend senior prom at her New Jersey high school but already owns an American women’s record. Athing Mu turned 17 last month, not long after she ran 600 meters in 1:23.57 at the U.S. indoor championships.

Mu is running the 800 meters here, hoping to beat her personal best of 2:01.38. She finished second in Thursday’s first round, running two laps in 2:01.95. On Friday, she was third in her semifinal heat in 2:02.47, qualifying for Sunday’s final. Mu has kept up with the country’s best despite a heavy workload, having won the Pan American Under-20 championships last week in ­Costa Rica.

“I just come into the race remembering that, whatever happens, I’m just doing this for fun,” Mu said. “I’m, like, the youngest person here. I have many years to come back and improve whatever I do now. Just have fun with it. . . . It’s crazy. I’m very, very proud of myself for working this hard.”

“It’s incredible,” said Ajeé Wilson, a fellow New Jersey native and the American record holder. “She’s super talented. The biggest thing is, she doesn’t have any fear when she goes out and races. She’s proven that she can hang with the best of us.”

Al Jennings has watched Mu since she was 5 years old, when she tagged along with her older brothers to the Trenton Track Club, which Jennings founded and has overseen for 46 years. At 9, she won an AAU national championship. At 12, she caught up to Jennings in height, on her way to a still-growing 5-foot-11. He has coached a handful of Olympians, and he said Mu is already the best runner he has ever seen — even though she still wears braces on her teeth and ribbons in her hair.

“Believe it or not,” Jennings said this week, “I’m still discovering about her that she is a very unique young lady, in every sense of the word.”

Mu’s parents moved to the United States from Sudan in 2000, two years before she was born. All six of her siblings dabbled in track, and some moved beyond the club: Her brother Malual is on Penn State’s track team and on full scholarship.

“Not only can they all run, but they’re all smart,” Jennings said. “I told her mom, ‘Whatever you guys have, we need to manufacture.’ ”

Mu tagged along at first, but soon she showed enough potential for coaches to take notice. She started traveling to big meets before she turned 10. While she piled up accolades, nothing prepared her for what happened after she won the national title in the 600 in February, when she held off a late charge from Raevyn Rogers, a six-time NCAA champion. At her next meet, she thought, “We’re definitely in a different phase right now.” Fans shouted her name. Reporters wanted to ask her questions.

“Media-wise and popularity-wise, I’ve noticed a lot more people actually know who I am,” Mu said. “When they see me walking, they’ll be like, ‘Oh, are you the one that’s on TV?’ Or, ‘Are you the one who ran that?’ I’m like, ‘Oh, yeah, that’s me.’ It’s just like, whatever. It’s just there.”

Mu has whittled down her list of colleges to five or 10. Apparel companies and agents have started calling, but for now Mu is trying not to listen. Bernice Mitchell, one of her coaches at the Trenton Track Club, thwarts calls from possible sponsors so Mu can focus on not only running but also school and her social life.

“She’s very adamant,” Jennings said. “She wants to enjoy her teen life.”

Soon, though, she’ll face decisions, including whether to go to college or turn pro, and how much she wants to shoot for the Tokyo Games. Jennings said he believes Mu can make the U.S. team next summer.

“That’s what I’ve been thinking for the last couple years,” he said. “She didn’t want to say that because that’s a boastful type situation. If you’re that good, you got to know you’re that good. She proved it when she set the American record.”