RE: So what I want to know is the data field a $ amount or a numeric figure representing the number of dependents? If numeric figure, how do we distinguish between qualifying child or other dependent?

No, it's a large dollar amount. 

For example if the employee had two children under age 17 and three children over age 17, they enter (2 * 2000) + (3 * 500) or $5,500 in box 3 of the form.  While the detail will be on the form for you as the employer to see, I expect that all you'll enter on the employee record in QB is $5,500.