Meet Sean Penn's New "Daughter"!

When Dakota Fanning learned she'd be playing Sean Penn's daughter in I Am Sam — opening Dec. 28 — she reacted like any seven-year-old would. "We had such a small apartment that there wasn't anywhere to run around," she recalls, "so I jumped up and down on the bed! And then I called my grandmother."

If Fanning keeps snapping up plum parts — she just wrapped Kevin Bacon's 24 Hours and is now shooting Sweet Home Alabama with Reese Witherspoon — the tyke will need a good long-distance plan! Of course, her thespian ambitions are no surprise to Granny. "I've been a ballerina since I was two," she smiles, "but I've always wanted to be an actress." Sometimes, though, she's taken her make-believe games to dramatic extremes! "I would go through 'childbirth' all the time," she says. "I'd put a pillow up my shirt and pretend that I'm pregnant."

Yikes! Fortunately for her, Mommy opted to take little Dakota to see a talent agent rather than a child psychiatrist. That wise judgement call paid off: The Broadcast Film Critics Association (BFCA) has just nominated Fanning — along with A.I.'s Haley Joel Osment and Harry Potter's Daniel Radcliffe — for best child performer.

She's taking her early success in stride, however, and is far more impressed by her newfound Penn pal. "[Sean] is very, very nice to me," she enthuses. "He took me to the Santa Monica Pier and lunch at The Ivy." While dining at the posh L.A. eatery, by the by, Fanning wasn't too shy to hit Penn up for a little career advice. "I wanted to be a cheerleader and a Brownie," she says of her past ambitions, "but when I grow up, I'd probably like to be a director."