A.D.
The Texas State Family Code dictates the following:
BASED ON THE MONTHLY NET RESOURCES OF THE OBLIGOR (the one obligated to pay)
1 child 20% of Obligor's Net Resources
2 children 25% of Obligor's Net Resources
the order of the children should have no bearing on who gets more. If two children have to be supported, the court will look at his income and if he is responsible for both children financially... take 25% of his net resources and apply any credits (for paying health insurance, etc.) and then should divide the amount equally between the two of you. Which means that he would probably be paying less to the other woman and he would then have to submit a petition to the court for modification of child support to get his obligation lowered.
Hope that helps. You can look the state family code up online if you need to - though sometimes it's hard to decypher unless you know what you're looking for.
Good luck... dealing with ex's is a real pain in the butt!