“Let the kids play.”

It’s an apt baseball slogan for 2019. The kids are playing, and in particular, they are hitting.

There are rookies who have taken Major League Baseball by storm, such as the Mets’ Pete Alonso, the Astros’ Yordan Alvarez and the Padres’ Fernando Tatis Jr. There are star sophomores continuing to rake, such as the Braves’ Ronald Acuña Jr., the Angels’ Shohei Ohtani and the Nationals’ Juan Soto. There are more experienced players who are still young enough to be rookies themselves, such as the Dodgers’ Cody Bellinger, the Astros’ Alex Bregman and the Indians’ Francisco Lindor.

All of those players are 25 or younger. They have joined many of their peers in immediately emerging as impact hitters, a phenomenon The Ringer’s Ben Lindbergh also wrote about recently.

Individual examples are one thing, but the overall numbers back them up. Young hitters have, in general, been improving over time. But they’ve never been better than in 2019, even adjusting for the current offensive environment.

There are different ways to define “young player,” and to assess their quality. They all tell pretty much the same story.

All stats entering Friday.

Lots of young guys are excelling

Through Thursday, there were 29 players in their age-25 season or younger who had:

• Collected at least 100 plate appearances.

• Posted a park-adjusted OPS+ of at least 120, or 20% above the league average of 100.

That group of 29 ranges from stars such as Acuña, Bellinger and Bregman, to less-heralded hitters, such as Twins rookie Luis Arraez and the Orioles’ Anthony Santander. It’s also the most such players to meet those criteria in a season in modern baseball history.

Most 25-and-under players with 100 PA, 120 OPS+
AL Era (Since 1901)
1) 2019 -- 29
2) 2015 -- 28
3) 1970 -- 24
4-T) 2018 -- 23
4-T) 1980 -- 23

While some of those 29 players could see their OPS+ fall below the 120 threshold between now and the end of the season, others also could join the group. That’s especially true in September, when rosters expand and more prospects get a shot.

Lowering the OPS+ bar to the league average of 100, there have been 50 25-and-under hitters who have reached that mark in at least 100 plate appearances. That’s within striking distance of the modern record of 58, set just last season. In fact, the past five seasons each rank among the top nine on that list.

Together, young hitters have never been better

It’s tough these days to be a hitter in your 30s. But pick any age below that, and offensive production is thriving more than it ever has.

Hitters 21 and under, led by Acuña, Soto and Tatis (now likely done for the season), not to mention Vladimir Guerrero Jr., are batting a collective .287/.368/.521 with a 129 wRC+, providing output roughly equal to that of Dodgers All-Star Max Muncy. That wRC+ figure -- adjusted for ballpark and league environment -- is easily the best in modern history.

The same holds true for nearly every age up through 29, with only the 25-and-under group not ranking first in wRC+. Instead, they are second (99 wRC+), behind a 1928 group that featured Hall of Famers such as Lou Gehrig, Jimmie Foxx, Mel Ott and Paul Waner.

Many top seasons for young hitters are similarly from baseball’s early days. Going back to when the sport was integrated in 1947 emphasizes how the aging curve has shifted of late, culminating in this amazing 2019.

Highest collective wRC+ for players 23 and under
Since 1947
1) 2019 -- 108
2) 2015 -- 105
3) 2007 -- 98
4) 1991 -- 97
5-T) 2018 -- 96
5-T) 2016 -- 96
5-T) 2013 -- 96
5-T) 2012 -- 96
5-T) 2011 -- 96
5-T) 1992 -- 96

A 108 wRC+ is well above the average of 100. Qualified hitters with a wRC+ in that range this season include Jose Abreu, Paul Goldschmidt and Manny Machado.

The feats are plentiful

Among the notable seasons for young players in 2019 (players listed with seasonal age, as of July 1):

• Bellinger (23) is leading National League position players in WAR and may be the favorite for NL MVP Award honors.

• Acuña (21) has a realistic shot at the fifth 40-40 season in MLB history.

• Soto (20) is enjoying a nearly unprecedented start to his career for a player so young.

• Tatis (20), if he does not return, will have become only the ninth player 20 or younger to have a season with at least a 150 OPS+ in 100 or more plate appearances. He would join six inner-circle Hall of Famers, plus Alex Rodriguez and Mike Trout.

• Alonso (24) has tied Bellinger’s NL rookie home run record (39), set two years ago, and could challenge Aaron Judge’s MLB record (52), also set in 2017.

• Alvarez (22) had one of the best 50-game starts for any hitter in baseball history.

• The Pirates’ Bryan Reynolds (24) is leading the NL batting race (.334).

It’s a list that could go on and on.

It doesn’t even include stars such as Bregman (25), Carlos Correa (24), Lindor (25), Ohtani (24) or Corey Seager (25). It doesn’t include 2019 breakouts such as Rafael Devers (22), Joey Gallo (25), Lourdes Gurriel Jr. (25), Carson Kelly (24), Ketel Marte (25), Austin Meadows (24), Yoán Moncada (24) and Jorge Polanco (25). It doesn’t include instantly productive rookies such as Aristides Aquino (25), Arraez (22), Bo Bichette (21), Guerrero Jr. (20), Keston Hiura (22), Brandon Lowe (24), Nate Lowe (23), Will Smith (24) and Alex Verdugo (23). Also missing are Ozzie Albies (22), Andrew Benintendi (24), Byron Buxton (25), Paul DeJong (25), Matt Olson (25), Franmil Reyes (23), Gleyber Torres (22) and several others.

That’s what baseball looks like in 2019. Each of the top eight position players in Baseball-Reference’s WAR, entering Friday, was 28 or younger. Twenty-nine of the top 33 were under 30, and 11 of those were in the 25-and-under crew.

The kids are playing, and they’re outplaying the kids of generations past.