Why Does First Born Get More Child Support?

I live in KY, but I was wondering why do children who were born first get more money in child support than the second born. I just do not think that is fair, it should be equal. The other child was born on DEC. 6th and my child was born on the 8th in the same year. So two days is ridiculous. Let me shed some light, the other mom gets $650 a month and I get $250. That is a big difference and since they are under three years of age they do not count in the mothers wages. If you know why these kind of laws are set in that the first born gets more money please tell me, i just find it fascinating that our government has done this.