"Hannah Montana" star Emily Osment is the subject of tonight's "20/20" when it poses the question: How young is too young?

How young is too young to pursue your dreams? It is a question that "20/20" investigates tonight, looking at child preachers, young boxers and child stars. The latter have been much in the news of late with former child stars, such as LINDSAY LOHAN and BRITNEY SPEARS, getting as much media attention for their stays in rehab as for their careers.

"20/20"'s CHRIS CONNELLY talks to EUGENE OSMENT, father of 15-year old EMILY OSMENT, who plays MILEY CYRUS' best friend on "Hannah Montana."

And, despite the fact that Eugene's own son HALEY was charged with DUI in 2006, he tells Chris he isn't concerned about his daughter growing up in the business: "You can find those kids even if you turn the camera to someplace else," he says. "I don't think that the industry is what makes bad things happen to people."

With Emily about to start filming a movie, having increasing requests for photo shoots and walking the red carpet, it sounds as if all the activity may be a bit much for a teenager.

But she tells Chris, "I'm so happy 'cause I've got stuff lined up every single day until next spring basically. And that involves friends and that involves work and school and anything. I love being busy. Busy is great."

Tonight, "20/20" premieres at its new time -- 8 p.m. ET -- on ABC with a look at "How Young is Too Young."