"I'm a pretty strict mom when it comes to sweets," the Oscar winner, 42, told PEOPLE at Tuesday's Eat Pray Love premiere in New York City. "Even though I have such a sweet tooth myself."
Roberts admits she only allows twins Hazel and Phinnaeus, 5, and son Henry, 3, to eat candy and junk food on special occasions. "You want sweets, ice cream and cake to be a great treat and a celebration," she says. "Something that's not everyday. I think this makes them appreciate it when they do have it."
While setting rules may be one facet of parenting accomplished by Roberts, her Eat Pray Love costar Richard Jenkins says Roberts is also an unconditionally caring and faithful parent.
"She's an unbelievably devoted mom," says Jenkins, 63. "She's in every scene of this film, and every time we cut for lunch, she went back to her kids and have lunch with them everyday. She's always happier on her way to see them, and the kids would light up when they saw her. She's the best."
As for sticking to her own limited sugar rule, Roberts doesn't necessarily practice what she preaches. "I'm not strict with myself," she says. "I cheat."