Several studies on skill acquisition now show that elite athletes generally practiced their sport less through their early teenage years and specialized only in the mid-to-late teenage years, while so-called sub-elites — those who never quite cracked the highest ranks — homed in on a single sport much sooner.

Data presented at the April meeting of the American Medical Society for Sports Medicine showed that varsity athletes at U.C.L.A. — many with full scholarships — specialized on average at age 15.4, whereas U.C.L.A. undergrads who played sports in high school, but did not make the intercollegiate level, specialized at 14.2.

We may prize the story of Tiger Woods, who demonstrated his swing at age 2 for Bob Hope. But the path of the two-time N.B.A. M.V.P. Steve Nash (who grew up playing soccer and didn’t own a basketball until age 13) or the tennis star Roger Federer (whose parents encouraged him to play badminton, basketball and soccer) is actually the norm.

A Swedish study of sub-elite and elite tennis players — including five who ranked among the top 15 in the world — found that those who topped out at as sub-elites dropped all other sports by age 11. Eventual elites developed in a “harmonious club environment without greater demands for success,” and played multiple sports until age 14.

The sports science data support a “sampling period” through at least age 12. Mike Joyner, a Mayo Clinic physician and human performance expert, would add general physical literacy-building to the youth sports menu: perhaps using padded gymnastics gyms for parkour, which is essentially running, climbing or vaulting on any obstacle one can find.

In addition to athletic diversity, kids’ sports should be kid-size.

In Brazil, host of this month’s World Cup, kids are weaned on “futsal,” a lightly structured and miniaturized form of soccer. Futsal is played on tiny patches of grass or concrete or on indoor courts and typically by teams of five players.

Players touch the ball up to five times as frequently as they do in traditional soccer, and the tighter playing area forces children to develop foot and decision-making skills under pressure.