An American obsession is attracting investments in baseball fields, volleyball courts and football camps, intensifying the gap between families with means and those without.

Josh Harris, a founder of the private equity firm Apollo Global Management, and a partner have been assembling one of the largest collections of youth sports properties in the country.

The youth sports industry, according to the Aspen Institute, generates about $40 billion in annual revenue, dwarfing other forms of entertainment. Last year, for example, the domestic movie box office grossed about $8.7 billion.

About 60 million children play sports, and the average U.S. sports family spent $1,016 on its child’s primary sport in 2024, a 46 percent increase since 2019, according to the Aspen Institute’s latest parent survey in partnership with Utah State University and Louisiana Tech University.

The private equity titans Josh Harris and David Blitzer are among those who see a big opportunity. Over the past three years, Mr. Harris and Mr. Blitzer used money from their family foundations to start Unrivaled Sports, which has been buying baseball camps, flag football fields and youth leagues to assemble one of the largest collections of youth sports properties in the country.