Child Support Calculator

When entering in the information on the Child Support Calculator it asks about your support obligations for other children then it also asks if you have any other children you are responsible for.

My ex has two kids that are almost grown that live with him some of the time. He pays their mom $300 a month in child support. Do I put the $300 child support and then show that he has responsibility for 2 other kids?

Correct, you need to put both the amount he pays and the number of children into the child support calculator.