“Liar Liar” actor Justin Cooper is opening up how his mom looked out for him as a child star … even protecting the “Little Rascals” actor from letters sent from prisoners.

In a recent interview on “The Not So Little Rascals,” Justin admitted … “My mom did a really good job of kind of shielding me from stuff.”

Justin said that his mother later spilled the beans when he was old enough about the prison mail he had gotten.

According to Justin … these letters would routinely involve prisoners telling him “about how they’re such big fans of me and I’m such a cute kid.”

Justin — whose credits also include the titular role of “Dennis the Menace” — said he “couldn’t really go anywhere in public” after Jim Carrey‘s “Liar Liar” was released in 1997.

However, the former child star said he “enjoyed it” and “thought it was cool.”