I would like to allow the person to add additional input field

I would like to allow the person to add additional children. i only want the extra fields for additional children to be added to a form, if the person filling them out needs them. How do i set that up with the fewest number of columns (so the response spreadsheet is not unwieldy to work with).

How about using the Dynamic Textbox widget?

This widget is a minimalist and will not take too much space on your form.

Demo form : https://form.jotform.com/61654058786972

The widget can be used in Calculation as well. The number of textbox added can be counted (it has a value of 1).

Let us know how it goes.

Thanks.