Brad Childress picked up the phone last spring to find Jared Allen on the other line. Childress figured he was calling to make small talk, and it started that way.

“He said, ‘How’s your family?’ and so we talked about that,” Childress said. “Then he says, ‘That’s not why I’m calling you. Have you heard about the new spring league?’ I said, ‘I think I’ve heard something about it.’ ”

Allen, a Vikings defensive end from 2008-13, had become an investor in the Alliance of American Football, which begins play in eight cities in February. He was calling to see if his former head coach would be interested in running another professional football team, something Childress hadn’t done since his 2006-10 tenure with Minnesota.

The answer was yes.

“Brad really enjoyed the idea of developing young talent,” Allen said. “So, I was able to talk him into it.”

In April, Childress was hired to coach the Atlanta Legends, and on Feb. 9 they will take the field at Orlando for the first of a 10-game season. It will be the first game as a head coach for Childress since Minnesota’s 31-3 loss to Green Bay on Nov. 21, 2010.

“I’m excited about it,” Childress said. “This should be a good product.”

Childress was an NFL assistant coach for much of this decade before retiring in January after five seasons with the Kansas City Chiefs under Andy Reid. That lasted a week.

When Chiefs offensive coordinator Matt Nagy become coach of the Chicago Bears, he convinced Childress to join him as a consultant — which is what he was doing when Allen called.

“I got back into coaching to teach young players,” Childress said. “… In a perfect world, I’d love to have all 50 of my guys get on an NFL roster next year.”

Offense rules

The league, brainchild of television producer Charlie Ebersol and former NFL executive Bill Polian, is being sold as a developmental league — a sort of Triple-A league for the NFL. The AAF owns all eight teams and has a television deal with CBS.

“There’s a reason and a spot for it because there is no more NFL Europe,” Childress said. “We don’t try to say we’re a rival to the NFL, we’re complementary to the NFL.”

It also is one of two nascent spring leagues, the other being the XFL, which plans to start again in 2020 after playing a season in 2001 and disbanding.

Childress’ Atlanta Legends roster is composed mostly of young players who were in NFL camps before being cut, but there are some NFL veterans. Atlanta’s top quarterback is former University of Georgia star Aaron Murray, who worked with Childress as the Chiefs’ third-stringer from 2013-15.

One of their top linebackers is Brandon Watts, a seventh-round pick by the Vikings out of Georgia Tech who played with them in 2014 and 2015.

Most of the league’s head coaches, though, aren’t up-and-comers. Other veterans include Orlando’s Steve Spurrier, a college legend and former Washington Redskins coach; Memphis’ Mike Singletary, a hall of fame linebacker and former San Francisco 49ers head coach; San Diego’s Mike Martz, who once took the St. Louis Rams to the Super Bowl; and former NFL coaches Dennis Erickson of Salt Lake City and Mike Riley of San Antonio.

Childress was the Vikings’ head coach when they went 12-4 and advanced to the 2009 NFC Championship. In his only stint as an NFL head coach, he was 39-35 before being replaced by his defensive coordinator, Leslie Frasier.

“He’s accomplished a lot as a head coach,’’ Allen said. “When I asked Charlie if he would be interested in Brad as a head coach in the league, he said, ‘Are you kidding me?’ ”

Allen played 12 years in the NFL and has known Ebersol since the early part of this decade. He was brought on board when the league began and is on the AAF’s Player Engagement Board of Advisers with former NFL defensive end Justin Tuck.

Allen said he doesn’t draw a salary and was brought in primarily to help promote the AAF. He said he was given a “sweetheart deal” to invest in the new league, saying it cost him less than $100,000.

“I was there to help give them some validity along with accomplished NFL players like Justin Tuck and (AAF head of football development) Hines Ward,’’ he said.

Allen said he likes some of the AAF rules that differ from the NFL’s, even if they don’t always favor the defense. Childress, a longtime NFL and college offensive coordinator, loves them.

“It’s going to be exciting,” he said. “Our games are going to be 2 1/2 hours. This is going to be rapid-pace football, no huddles. You’re going to have a 30-second clock (rather than 40) and you’ve got to go for two points every time.

“There are no kickoffs, and if you want to try an onside kick, it’s like going for it on fourth-and-10 at your (own 35-yard-line).”

Opening doors

The Legends will play at Georgia State Stadium, which seats 36,000. The venue is scaled down from when it was Turner Field, the Atlanta Braves’ home from 1997-2016.

The AAF’s emphasis on development extends to assistant coaches. While Childress’ defensive coordinator is Kevin Coyle, 62, a longtime NFL assistant, his offensive coordinator is Michael Vick, whose career as an NFL quarterback was overshadowed by a 21-month stint in federal prison after he pleaded guilty to involvement in a dog-fighting ring.

Allen said Vick, who starred for the Atlanta Falcons from 2001-06 and is coach for the first time, was vetted before being hired. “He’s repaid his debt,” he said. “He’s grown as a person. This league is about opportunity, and not just for players but for coaches, as well.”

Also on Childress’ staff is defensive specialist Jen Welter, who in 2015 became the NFL’s first female assistant coach, leading the Arizona Cardinals’ linebackers on a six-week internship for training camp and the preseason. Welter met Childress before her first preseason game, when the Cardinals played the Chiefs, and they stayed in touch.

“She’s a doctor of psychology, and my degree is in psychology and I’ve used it every day I’ve been in coaching,” Childress said. “She has a background with linebackers. She’s very up with what’s going on in football. It will be a different way to approach it with our players.”

Welter, a former linebacker and coach with the Texas Revolution of the men’s Champions Indoor Football League, is one of three women assistants in the AAF. “I think the league is pioneering, which is so exciting to be a part of,” she said. “(The league is) giving people a reason to continue to open doors.”

Welter was hired early this month. It didn’t take long for her to see how many hours Childress works.

“I don’t know if morning and night are separated in his book,” she said. “They all seem to blend together. I’ve shown up at 6 a.m. and he’s in there before me. I’ve left at 10 p.m., and it’ll be, ‘Coach, I’ll see you tomorrow.’ He might be super human in his lack of sleep. … He inspires everybody around him through that work ethic.”

‘A lifer’

Quarterback Tarvaris Jackson saw that work ethic while playing for the Vikings during Childress’ entire tenure. Jackson, an assistant coach at Alabama State, has stayed in touch with Childress and said he’s not surprised to see him take over the Legends.

“He’s a lifer,” he said. “He just loves to coach. He’s got a lot to offer. He’s a very intelligent guy.”

Childress still has a home in Mound, where he spends time during the warmer months. His daughter and her husband work in the Twin Cities, and he has three grandchildren in the area.

He continues to keep tabs on the Vikings, which includes occasionally checking in with head athletic trainer Eric Sugarman, whom he hired when he arrived in 2006.

The Vikings (8-6-1) can still make the playoffs two ways: beat Chicago (11-4) on Sunday at U.S. Bank Stadium, or have Philadelphia (8-7) lose at Washington. The Bears (11-4) have wrapped up the NFC North title, making Nagy, 40, a strong candidate for Coach of the Year after taking over a team that went 5-11 last year.

Childress was only with the Bears for three months, but Nagy gives him some credit for helping him adjust to his new job.

“Him coming in and helping out, we called it the ramp-up system,” Nagy said. “He was able to come here and I had a lot of different duties as a first-year head coach that would pull me away from some of the stuff offensively. And he was able to just hold it down for me with a lot of new coaches on the offensive staff, so I appreciate that.”

Childress said he enjoyed working with Nagy, with whom he worked for all five of his seasons in Kansas City. An added bonus was returning to the Chicago area, where he was born and raised. But the lure of being a head coach again was too enticing to turn down, and he isn’t waiting for a call from an NFL team.

“I don’t think my demographic fits anymore,” he said. “It used to be that they were recycling the (Marty) Schottenheimers and (Dave) Wannstedts and (Dick) Vermeils and those guys, but that’s not the case anymore. Everybody’s looking for a Sean McVay (the 32-year-old Los Angeles Rams coach) or hiring a Matt Nagy. They’re certainly not looking for a 62-year-old.”

But the AAF was. Childress, in fact, is just the fifth-oldest coach in the league. Spurrier is 73, Erickson 71, Martz 67 and Riley 65.