Sean Penn can't keep his hands off Charlize Theron

Los Angeles - Sean Penn couldn't keep his hands off Charlize Theron in Los Angeles on Friday.

The couple - who made their first public appearance together three weeks ago after getting together late last year - were spotted kissing passionately as they drove around Beverly Hills in a dark SUV.

A source told E! News that the South African beauty, 38, and Milk star, 53, "made out the entire time" when they were forced to pause at a stoplight while running errands.

The eyewitness said that Charlize's two-year-old son, Jackson, was not with them.

An insider recently claimed the couple are already talking about getting married and the Oscar-winner, who has two children, Dylan, 23, and Hopper, 20, with his ex-wife, Robin Wright, has expressed interest in adopting Jackson.

Sean is a totally different person

The source said: "Sean is head over heels in love with Charlize, and her son Jackson.

"He is a totally different person around Charlize, she brings out the gentle and fun side that not many people have seen of Sean. To see this previously surly grown man, romping around Charlize's backyard with Jackson, with a smile on his face would amaze Sean's detractors. Charlize is getting Sean to not take himself to seriously.

"The two began talking about marriage in the last few weeks, after Sean moved into Charlize's house. She has never wanted to get married, but seeing how Sean interacts with Jackson, she is having a change of heart.

"For the longest time, Charlize thought it was just going to be her and Jackson, and she was OK with that. For her to now be talking about getting married is a huge departure for Charlize."