I run a small talent agency, which occasionally does get jobs in for children (www.j-cast.biz). Mainly though, adults.
My children are also registered with the usual children's modeling agencies: Sugar and Spice, Avocado, Junes, etc. (all of these agencies are easily google-able).
Modeling can be a fun, OCCASIONAL experience, but I would not recommend trying to make a career out of it for your kid, unless they really are begging to do it. For me, it's a once or twice a year ordeal for fun material (such as carseats or conservative preppy clothing), for nice keepsakes.
Here are my experiences with children's modeling:
Something new to do
Can meet new people
Extra cash for college tuition or however you choose to spend
Pictures are great keepsakes (IF you can make sure the agency gets them to you!)
Hard to get to the auditions, especially if you have more than one child
Shooting hours can be long
No strict child-labor laws here it seems
I heard a story of a boy who did so much modeling, that the flash damaged his eyes and he now has thick glasses. Moderation is the key.
Some agencies put the child's first and last name next to their picture on their HP, for the world to see. I would ask that their full name NOT be displayed at registration. Call me overly-protective, but I think this is a very reasonable request and a condition for registration.
Things to be aware of:
Negative experience 1:
On my most recent shooting for an Aprica car seat advertisement, I was reminded why NOT to enroll my kids in these things. I was asked to show up in the morning, but had to wait for 3 and a half hours, while they shot the ADULT models first. (?!?!). It's a Japan-thing. Older people get the respect.
They decided to shoot at nap-time and my son was cranky. It was not a good experience and the client was complaining about my son not smiling. Hmmm... I wonder why?
Have a look at the photo on top: Does my son seem very happy about being there?
Positive experience 1:
On another shoot, last year for Combi mini, it was an excellent experience. The client provided toys, snacks, plenty of space for the kids to play, and took the kids who were in the good moods first, not sticking to their strict schedule. This is how it should be done.
Positive experience 2:
My daughter had a shooting a few months back for a conservative Japanese clothing brand, winter/fall clothing. The client hired a lady, whose job was solely to entertain my daughter. She brought games, flashcards and was just buddy-buddy with her the entire shoot. My daughter had such a great time and still asks to play with that lady. Some clients just get it. Some don't.
In short, it depends on the client. It depends on your kid. It depends on your lifestyle. It depends on you.
But because it is hit or miss, try to make your conditions known upfront. What time do you need to leave? Nap time? Where to send the copy of the completed project? Etc. But, if you are too overbearing, you do risk not being cast for future jobs. Is that important to you? Is a one-time thing ok for you? Everything in moderation.
On a positive note, it can be fun and a great way to socialize (why not go to a big kids group and get paid, and also with photos in the end?) It's great to send to Grandma. But, don't go overboard. Kids should be kids. Education should be first. In the end, it is your decision.
What you can do to make your experience better:
With my agency, I talk to the client ahead of time and make sure that the children are put ahead of the adult models and have a clear start and finish time. It is not fair for the kids to make conditions clear beforehand. I think this should be the agency's job, but since they don't usually do this, it is up to us moms.
When I am going with another agency than my own, I always give a specific time that I need to leave, so I can prepare instead of just guessing on the time. I suggest to bring lots of books and try to think of the waiting time as a chance to spend quality time with your child.
Before the audition:
Ask in advance to the agent what chance your child has at getting the job, to judge whether or not it is worth it to go to the audition. If you do want to do occasional modeling, you need to show up to auditions and keep in good communication, with updated photos to the modeling agency. Make sure that the content is something that you approve of (i.e. no tiny mini skirts for little girls, etc.)
My favorite agency is Sugar and Spice. They always give me the material that my children modeled in. If the agency has not given you the material, keep bugging them. Weekly. Otherwise, your entire effort is wasted.