Return to sender. Child star Justin Cooper, whose claim to fame is playing Jim Carrey’s son in the 1997 film “Liar, Liar” when he was 8 years old, revealed in a recent interview on the “Not So Little Rascals” podcast that he received disturbing fan mail from prisoners when he was just a kid. “My mom did a really good job of kind of, like, shielding me from stuff, you know,” he told co-hosts Jordan Warkol and Blake Collins (who starred in 1994’s “The Little Rascals”) when asked if there were any “overwhelming” or “scary” moments of childhood fame. “She would tell me later on about, like, prison mail that I would get that she never showed…