E.,
I understand your concerns. But from experience that other friends have had... he would be the one to have to go back to court and usually the only way the judge will allow a reduction is if his income (net income -after taxes - from his job) has dramatically changed. Just because he had decided to have another child does not mean his obligations to his other children changes. Two men who work with me have multiple children with different women, and they pay alot of child support because of it. (1 has 2 children with ex wife and 1 child with ex girlfriend- the amount he has to pay is not adjusted because they are with different women- he actually pays more because in TX the first child is 15%, and each child after that 5% up to 25% of net pay - after taxes. So he pays 20% to his ex wife and 15% to his ex girlfriend)
So I would suggest going on line or contacting your divorce lawyer and just asking what your state mandates are for child support. You probably have nothing to worry about. Let him pay for the court costs to go back to court... because then the costs would be on him not you. Just be armed with information before hand. You might even send him a copy of whatever you find so that he can make the decision not to persue it. Because if it is found that he is making more money then when the child support was ordered, he could wind up paying more. Wouldn't that be poetic justice!
The girl in my office had that happen, they went back to court for a review, he was sure it would be lowered, but it was actually raised.
Hoping the best for you.
D.