What is a fair modeling fee for a picture of my child used for the advertising of a business?

[CAPTMIAMI]

[YahooDeana]

It depends on what the company can afford.

Is it for a non profit? A local clothing company or a franchise like Bloomingdale's?

Super Models on "Sports Illustrated" make a whopping $200 per day for their photo shoots.
They take low pay (they probably normally charge $10,000 per day) because of the publicity.

All that is relevant.

[Kittysue]

What sort of business?
How big are they?
How will the picture be used - newspapers, billboards, in-store posters, website, etc?
How long do they want to use the picture?
Where is the business located?

These are all factors that go into determining a model's fee

A major international retailer like Gap using a picture in ads that appear in national magazines could pay up to $15,000 for a child model in a Gap Kids ad
A local clothing store or photo studio in a small town that might advertise in a local newspaper and on their website might pay $200

They should be telling you their budget and fee, not the other way around. Normally the booking client determines who much they are paying and you have the chance to agree or not