"I wasn't really interested or curious about talking to the kids because they were so young at the time," Schwimmer told PEOPLE during the FX Winter TCA Press Tour on Saturday in Pasadena, California.
"I was more interested in finding my way into Robert as a character, and who he was as a husband and as a father and as a man," he added.
However, Schwimmer, 49, did talk to the Kardashians' mom, Kris Jenner.
"Kris was really, really generous with her time," the Friends alum shared. "It was really great to learn about how much a man of faith he was and how loyal and considerate he was. He was a very humble, very private person. Not at all seeking the limelight, that was inadvertent."
Director Ryan Murphy also opened up about the Kardashian children's lack of involvement in the 10-part miniseries.
"In the 10 episodes, there are over 400 scenes that were written, and of those 400 scenes, only four or five of them involve the Kardashian children," Murphy explained during a panel. "So I think that gives you sort of a grasp on how important we felt they were to the story."
American Crime Story: The People v. O.J. Simpson premieres Feb. 2 at 10 p.m. (ET) on FX.
Reporting by CHRISTINA DUGAN