D.C. United’s training session had a noticeably younger look Wednesday — and not just because some academy players joined the first team for a morning workout and captain Dwayne De Rosario was on a stationary bike rehabbing a hip injury.

Collin Martin, 18, was christened as the club’s newest homegrown player after signing a pro contract this week. Jared Jeffrey, 23, participated in his first practice since being acquired from the German circuit last week. Luis Silva, 24, was in black-and-red duds after arriving from Toronto on Tuesday.

Alain Rochat, 30, was long gone — sold to a Swiss club this week after expressing dissatisfaction with MLS’s trade policy and subsequent move to Washington from Vancouver last month.

The addition of Martin, Jeffrey and Silva reinforces United’s plan to go mostly young and go mostly American in an effort to reverse course after a woeful first half to the MLS season.

“It’s not across the board, but I do think we want to continue building our base of quality young Americans,” Coach Ben Olsen said.

That young American base includes goalkeepers Bill Hamid (22) and Joe Willis (24), defenders Ethan White (22), Chris Korb (25), Conor Shanosky (21) and Taylor Kemp (22), midfielders Nick DeLeon (22) and Perry Kitchen (21) and forwards Chris Pontius (26), Casey Townsend (24) and Michael Seaton (17).

“We are always going to have foreigners in this team and they are always going to help us,  but we’re in a situation now where we can build a base over the next year or two and make sure we don’t have dips like we’ve had up to this point. Part of that is our depth, and guys like Silva and Jeffrey will help us with that. In essence, the American thing doesn’t have too much stock in it, just more reliable depth.”

Silva, acquired for an undisclosed amount of allocation money, brings the most potential for immediate impact. After a standout rookie season in Toronto, he was not as productive this year. Nonetheless, Olsen sees a dynamic young player who will lift the dreary attack (eight goals in 19 league matches).

“He brings a vision a lot of our guys don’t have,” he said. “We have one or two guys [now] who can make the last pass, pull off different ideas that maybe can help us in the offensive end with our lack of productivity.”

Silva and Jeffrey, a two-way central midfielder with youth national team experience, are almost certain to debut in Friday night’s friendly against Chivas Guadalajara at RFK Stadium. Olsen might also use Martin, a lean attacker.

“Sure. I want to get him in right away,” he said. “I still have to evaluate who is available and what it is going to look like, but I have no problems putting the kid in there. He turned pro.”

Beyond this week, Martin could end up on loan with the third-division Richmond Kickers, joining Seaton, “but it’s late [in the USL season] and they are in a good rhythm,” Olsen said. “That is something we will discuss” with Kickers Coach Leigh Cowlishaw. “The training alone here [in Washington] is going to move him along at a good rate. If we can move that further with games with Richmond and Guadalajara, all the better.”

So where is Rochat? Olsen steered questions to General Manager Dave Kasper, who did not want to comment. The Insider reported Tuesday that United has sold him to Swiss club Young Boys for more than $500,000.

After playing 2 1/2 seasons in Vancouver, Rochat was not happy about uprooting his family. Ultimately he decided to pursue a move to Europe. His wife gave birth to their fourth child last week.

At the time of the trade, a source close to the situation said, United was not aware Rochat was reluctant to switch clubs, countries and coasts. “He really wanted to go back” to Europe, the source said. Rochat declined United’s contract extension, the source said.

In the end, United received a healthy infusion of cash for a 2015 second-round draft pick (which was sent to the Whitecaps in the Rochat trade).

“He was public in saying his dissatisfaction with the MLS protocol [for trades], and you don’t need to talk to a guy to know that’s tough,” said United midfielder John Thorrington, Rochat’s teammate in Vancouver the previous two years. “It’s not easy when you have a wife that is pregnant and you are called in and told you have to move across the continent.

“He was very good for D.C. He had the right attitude in training and games. Despite any dissatisfaction he made public, he was fantastic in the locker room. He had to do what was right for his family and his career.”

Silva said he was “shocked” about being traded by Toronto. “I still am.”

Silva, who is from Los Angeles, was preparing to begin practicing Tuesday when Toronto officials summoned him to the offices. He packed two bags and was on a plane to Washington a few hours later. (He’ll return to gather the rest of his belongings this weekend.)

“I don’t hold a grudge. I thank them a lot for drafting me” fourth overall in 2012. “This is my team now and I am happy here.”

Silva and Pontius were teammates at UC Santa Barbara in 2008, and Silva played four years at UCSB with Pontius’s brother, Tim.

“He was feeding me a lot of my goals,” Pontius said, reminiscing about his senior year when Silva was a freshman. “He can find players running off the ball. He has good vision. He has good feet. He is technical. We have struggled to link up — you can see that in our goal production. It’s a big role, but hopefully Luis can step in and be a playmaker for us.”

Is Silva the answer?

“I am an attacking midfielder, and if I get the ball at my feet, I can make things happen,” he said. “I can score. I can set up people. That is my football. Unfortunately, back in Toronto, we didn’t play with an attacking midfielder, so hopefully here they use me in the right position and right spot.”

Jeffrey, a Texas native, is adapting to a new city, club and league after moving to Europe after high school. He played with several United players on the youth national team level.

He had weighed an option in the German second division (after spending three years in the fourth tier with Mainz’s reserves) but decided to come home.

“MLS is a lot different than it was five years ago,” Jeffrey said. “It is really growing. I see a lot of my friends doing well and enjoying it, and I wanted to be a part of it.”

Martin, a Bethesda-Chevy Chase High School graduate, turned pro after playing one season at NCAA power Wake Forest.

“Very excited and nervous the first day — unusually more because today was a special day,” he said.

Martin said he decided to leave Wake about a week ago. He discussed his future with Demon Deacons Coach Jay Vidovich before committing to United. Terms of his contract were not disclosed.

“I thought it was a good time for me, a good time to get started.”

An update on trialists coming soon …

Guatemalan defenders Cristian Noriega and Jaime Vides, from Municipal, began trials today. Noriega, 26, has 27 caps and appeared in five 2014 World Cup qualifiers. Vides, who turns 26 this week, has seven caps.