Sean Penn, Charlize Theron Heating Up

Sean Penn appears to be turning into Mr. Softie.

The reputedly gruff actor has been showing his softer side lately when it comes to new girlfriend Charlize Theron and her 3-year-old son Jackson.

Sunday, the 53-year-old actor was all smiles during an outing with Theron, 38, and Jackson at the Underwood Family Farm in Moorpark, Calif. Penn could be seen with his arms wrapped around Theron, nuzzling her neck, and playing the doting dad to Jackson, whom Theron adopted as a single mom.

Two days earlier, the new couple also engaged in a serious public display of affection.

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This time, the South African beauty was seen cupping Penn's face during a passionate kiss in the front seat of her car.

A source told E! News that the pair, stopped at a traffic light, "made out the entire time."

Perhaps in a sign of how smitten he is, Penn was photographed earlier in the day following behind Theron as she left a nail salon, wearing flip flops and carrying her shoes in her hand.

But Penn's affection isn't reserved just for Theron.

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The father of two grown children, with ex-wife Robin Wright, was seen cuddling with Theron's son Jackson during a beach outing last week. Before that, he was snapped making silly faces at the youngster during a grocery-store expedition with Theron in January.

The two Oscar winners went public with their romance at Penn's Jan. 11 Help Haiti Home gala, where they could be seen getting cozy with their arms around each other. Later Penn called her a "keeper," after Piers Morgan congratulated him on Theron.

According to Morgan, Penn told him, "She's a keeper, that's for sureā€¦ well, I'll do my best to keep her anyway."