Is it possible to build a registration form to calculate and process payments?

4. Is it possible to build a registration form that has an option to "add another child" so that when the user clicks a button it expands the form to register another child? Also, if another child is added, is it possible to program the form such that it calculates the total cost based on the total number of children?

Your requirement can be achieved by duplicating the fields of the child information for the number of children that you need want to register. That means, if you want the form to allow 10 children to register, you can duplicate the required fields to be collected for each child 10 times on the form. You may show/hide the information by setting up some conditions as mentioned in the guide below:

https://www.jotform.com/help/297-Show-or-Hide-multiple-fields-at-once-using-form-collapse-tool

You can perform calculations on the form by using the Calculation widget and pass the calculated result to the payment field in order to process the payment.

https://www.jotform.com/help/275-How-to-Pass-a-Calculation-to-a-Payment-Field

Hope this information helps!