Alot of them start when they are really little with like commercials and stuff and eventually they’ll either audition for a movie or a talent scout will find them.

most of them start in commercials or have crazy parents who move all the way to hollywood or NYC to make there kid famous.
MK& ASHLEY started out in full house
RAVEN SYMONE: bill cosby show
HILARY DUFF: jasper meets wendy? i think
TAYLOR MOMSEN: commercials and the grinch who stole christmas (real version) she played cindyloo

you could check it out here http://watch-movies.net.in. This site has so many video. A nice site for new releases.

you could try it on http://watch-movies.net.in. Excellent site for new movies. They got loads of good stuff