Alex Bunbury, a Canadian national team forward, finished his career with Kansas City in 1999-2000. His son, Teal, bottom right, was in elementary school at the time and frequented Arrowhead Stadium, the club’s home for 12 years. (Ed Zurga/Getty Images)

Major League Soccer will enter its 18th season Saturday, a passage into adulthood after growing pains and a moody adolescence. As part of the evolution, the children of the league have also matured, forming a second generation of players and coaches.

Three sons have followed in their fathers’ footsteps by playing in MLS: Sporting Kansas City forward Teal Bunbury, Columbus Crew midfielder Konrad Warzycha and Portland Timbers forward Jose Valencia.

Since the league’s launch in 1996, several familiar names in American soccer have surfaced in the college playing and coaching ranks, in MLS youth academies and even in the agent business.

Their career paths were influenced by exposure to the sport at an early age: kickarounds during summer vacation while practice sessions took place, visits to locker rooms before and after matches, road trips for big games.

“It was like the coolest place on earth for me,” Ken Arena, 32, said of teenage years spent at D.C. United’s old training grounds in Herndon.

Arena’s father, Bruce, was coach from 1996 to 1998 before he accepted the U.S. national team post. Ken played at Oakton High School and the University of Virginia and was in MLS for three years. Assistant coaching jobs at U-Va., George Mason and UCLA led to the head position at Florida International University last year.

The younger Arena wasn’t without peers at United Park. The kid corps there also included Michael Bradley, son of then assistant Bob Bradley. Michael, a former MLS midfielder, now plays for Roma in Italy’s Serie A, one of the world’s most prestigious leagues, and started for his father on the U.S. national team at the 2010 World Cup in South Africa.

James Moreno was a toddler back then, watching his father Jaime become an MLS legend. James now plays for United’s under-17/18 squad. Another tot at the time, Ian Harkes, son of former D.C. and U.S. captain John Harkes, is bound for ACC power Wake Forest this fall.

Also in attendance was assistant coach Dave Sarachan’s son, Ian, who went on to play at Illinois-Chicago and now coaches in the Los Angeles Galaxy’s academy.

Christian Onalfo, son of former United player and coach Curt Onalfo, is a top prospect in the Galaxy’s academy.

But the first two-generation players were the Bunburys. Alex Bunbury, a Canadian national team forward, finished his career with Kansas City in 1999-2000. His son, Teal, was in elementary school at the time and frequented Arrowhead Stadium, the club’s home for 12 years.

“It was a culture to me,” Teal said last week. “I appreciated it and welcomed it. To be brought up in something like that, it fueled my desire to be professional and be in this league. When I saw it, I wanted to be part of it.”

Bunbury, 23, remembered messing around after practice with Kansas City players Peter Vermes and Kerry Zavagnin — role models then, his bosses now. Vermes is the club’s coach, Zavagnin an assistant.

Like many athletes, Alex Bunbury pushed his son to succeed athletically.

“But if I hadn’t been pushed as I was, I don’t think I would’ve made it to where I am now,” said Teal Bunbury, who left the University of Akron after two years and was the fourth overall pick in the 2010 MLS draft. “With his knowledge and guidance, it led the way for me.”

Warzycha followed a similar path but with broader experiences. His father, Robert, was a stylish midfielder in their native Poland, then England and Hungary before ending his career with a seven-year stint in Columbus. Robert then became a Crew assistant coach and accepted the top job in 2009.

Konrad, 24, starred at Ohio State before spending a year as a Kansas City reserve. His father invited him to Crew training camp this winter and signed him this week.

“I always looked up to him, not only as a dad but as a player,” he said. “I wanted to play pro like him. To follow in his shoes, it means a lot to me.”

Childhood experiences during United’s early years have become permanent memories. Michael Bradley recalled cleaning muddy cleats for a few bucks. He and Ken Arena created a mini-field with wooden benches tipped on their side to serve as barriers. Families would gather at players’ houses.

“Jaime [Moreno], Marco [Etcheverry], [Jeff] Agoos, Eddie Pope — it was like my posters came to life and spoke to me,” Arena said of United’s championship lineup.

While MLS’s second generation rises throughout soccer, the next one is beginning to arrive: In January, Michael Seaton signed with United. He was born on May 1, 1996 — 25 days after the league’s inaugural game.