The beautiful thing about women is that we have awesome intuition. The bad thing about women is that we don't always listen to it. I do modeling and print work every now and then, so let me say that you need to RUN not walk away from this situation. Anybody can post an ad on Craigs list and say they are a modeling agency. Why on earth would you need to bring the clothing for a modeling shoot? That defeats the whole purpose. Advertisers already have their clothes picked out then they pick the models. They are looking for tweens then they bring their own clothes??? Serious red flag and definitately not a good situation in the least. I can't possibly know the specifics of how this is bad and you shouldn't go to find out. Just know that it's bad.
Look in the phone book under Talent Agencies. Call and find out if they have open casting calls. Some will say a certain day of the week for open calls to see if they are interested. If they like your child then you'll need to get headshots, that's it. You don't need to sign a contract. I work with two agencies on my own free will. No one would ever have someone sign a contract without seeing them in person. Sounds amateur and desperate.
There are pedophiles always looking to add photos to their collection. Please stay away from this situation, and go a more traditional route. It's up to you to know what's right and protect your child. They go where you lead them. Please don't lead them here. Craigs List is too sketchy.
Good Luck!