Shawn Southwick's accusing Larry King of cheating, according to sources, but months before the divorce it was Shawn facing cheating allegations...with a little league coach who admitted, on camera, that "mistakes" were made.

Hector Penate -- actor and former baseball coach to Larry and Shawn's sons -- spoke to a TMZ cameraman last September about the alleged infidelity. Hector's not-so-cryptic answer: "one thing led to another..." 

Shawn denied anything went down...but ya think Larry's lawyers want to talk to this guy?