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Teresa Giudice is expected to report to prison to start serving her 15-month sentence for federal fraud crimes on Monday, Jan. 5. But when she gets locked up, her youngest daughters won't know the real reason why Mommy is gone, a new report alleges.

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According to Radar Online, the "Real Housewives of New Jersey" star and husband Joe Giudice -- who will serve his 41-month sentence on related crimes once Teresa gets out in 2016 -- told their two youngest daughters, Milania, 8, and Audriana, 4, that Teresa "is going away to work," said a source.

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The reason for the lie? "Teresa and Joe feel that they are too young to fully comprehend what is going on," the source told Radar. A second insider added that Teresa specifically told her youngest girls that "she is going to jail to work on a book about jail."

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The couple's two oldest girls, Gia, 13, and Gabriella, 10, however, "do know where Teresa is going," the first source told Radar. Gia seemingly commented on the situation facing her mother -- whom she recently called "my best friend" -- and their family on social media. "Can't sleep, [too] much stuff on my mind," the teen tweeted early on Jan. 3.