1st I wouldn't look at competing with your neice. A fit model is someone who tries on the clothes for the designers and other various staff to see if the clothes fit properly on a live person. so she was basically a mannequin. (I did the same job for Target and Marshall Fields) It's good money, but I can't imagine that it is much fun for a child.
Plus you have to stand there in your underwear for them to measure you every couple of months to make sure that you are still the same size they want to fit.
I am not sure who I would go to, to trust my kids with.
I know that you should stay away from the temptations of John Robert Powers- they are simply a school and want to charge you upwards of $6000 for a 3 year old kid to learn about being a model. It's a rip off. You will go there, they will tell you your kid has made the cut; then you get excited, then they want you to spend tons of money for schooling! They have even been investigated on, I believe, it was channel 9 within the last year or so.
SOme that have been in the industry for a long time are: Caryn's, Akerlind Steele (I think they may have changed name though) they are a good casting company in Mpls., I know there are a couple of others, but my brain is fried right now.
I wish the woman I was with was still in business, she was very familiy oriented and I trusted her.
anyway, it's not all it's cracked up to be. sure it's awesome money to start stocking away for college; but if this isn't your thing, and you aren't comfortable parading him to audition after crazy audition, it may not be for you and your son. Even if he is a little cutey pie. there are many cute kids out there, and he and you will have to deal with rejection too.