SEAN PENN’s grown children don’t like his new girlfriend Charlize Theron and have secretly nicknamed her “Chuckles” because she constantly cracks jokes in a futile attempt to win their approval, a source says.

As Hollywood’s latest May-Decem­ber couple inch closer and closer to walking down the aisle, a source says the one stumbling block is that Sean’s children by ex-wife Robin Wright – daughter Dylan, 22, and son Hopper, 20 – haven’t warmed up to their soon-to-be stepmother.

“Sean is crazy about Charlize and can’t wait to marry her, but he’s getting incredible flak from his kids,” a Hollywood insider told The ENQUIRER.

Dylan and Hopper find the gorgeous South African actress “shallow, dense and vapid” com­pared to their actress mom, who is every bit Sean’s intellectual match and worked on his political causes and charities, the source says. In sharp contrast, Charlize is from a small farming town and dropped out of high school to become a model. Although she went on to win an Oscar and Golden Globe for her performance in “Monster,” Dylan, a budding model, and Hopper, a college student and actor, are not impressed. “They latched onto her shortcomings and feel there’s no way she can fill Robin’s shoes,” said the insider.

Robin, 47, is now engaged to 14-years-younger actor Ben Foster, who is adored by the Penn kids. But while they have no problem with Robin’s “cou­gar” image, they seem to resent that Sean, who is 53, is dating a 38-year-old.

Unfortunately, Charlize got off on the wrong foot when she first met the Penn offspring and tried too hard to befriend them, according to the source. “She insisted they call her by her nickname, ‘Charlie,’ and tried talking about the music and films she thought they’d like. She cracked jokes, but the kids ended up laughing AT her instead of with her.” 

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