Where Hollywood babies come from

Where else? From agents and managers. Given the box office success of the Judd Apatow comedy, "Knocked Up," Slate's Explainer column takes up the subject of newborns in the movies. Basically, infants in California can start working when they're 15 days old, provided that they have a work permit and a note from a doctor stating the baby is "physically capable of handling the stress of filmmaking." The most desirable infant actors are twins or triplets that can be swapped out.

There are a slew of other regulations outlining what film crews can and can't do with a baby. In California, infants under 6 months are allowed on-set for two hours a day, but their actual workday can't exceed 20 minutes. For every three children of ages between 15 days and 6 weeks, there must be one nurse and one studio teacher; California law also requires that a parent or guardian be in attendance. Most productions set up trailers equipped with cribs where babies remain with their parents, guardians, and nurses before their scenes.

Don't expect much for the old college fund. Babies are typically hired as "background actors" at a day rate of $126, although if the baby's agent is good enough, that could increase to $737 as a principal performer.