You have to be available with a very short notice to go on auditions or shoots usually.
NEVER ever ever pay anything, if they want you they will pay you. The only exception is you will usually need to pay a photographer and come up with a portfolio of photographs.
Caryn and Moore are the only legit agencies I know of in MN.
I tried to get my daughter into modeling as a baby and eventually gave up. My daughter is now7 and I still get the "you should put her in modeling"
They look for kids that stand out, something special or different about them or a child that's very unique looking and sticks out. A red head with freckles or very intriguing eyes etc. The child also has to be very photogentic not just adorable. Some people look great in realife but not that great photographed. Look at a Target ad it's not just the cute little caucasion blonde hair blue eyed kids anymore its' really changed alot. Biracial children with different mixes are really popular now days.