California law requires it: Infants need a doctor's note and legal permits before they can be stars. They're only allowed on camera for 20 minutes a day. They must be accompanied by both a nurse and studio teacher — both paid for by the producers. The babies also need to be at least 15 days old.

But the filmmakers behind "Babies," a documentary in theaters Friday, say they didn't have to worry about all that. They cast the film's four international stars while they were still in the womb and filmed them unobtrusively in their natural environments, like "a wildlife film of human babies," says producer Amandine Billot. Read More