When a couple breaks up, regardless of whether they were married or not, their financial states are likely to be very different. One may have gotten the lion's share of the assets they had while together, like money in the bank and the house. The other may have greater earning power due to having focused on his or her career while the couple was together. Often, the one with less earning power typically winds up getting paid money by the one with more earning power.
The money, classified as child support, is to go to the expenses of the couple's children. In many cases in past few decades, the higher earner was the father of the children and he would up paying child support to the mother of the children. This was all the more common because the mothers were typically awarded primary custody of the couple's children. However, things are changing in society step by step.
Now fathers are making the case that they are fully capable of raising their own children and merit primary or joint custody. When they get that, a secondary effect is that child support dynamics change. If a father has primary custody of the couple's children, their mother may be ordered to pay him child support so she can be contributing to their upbringing, at least financially.
Interestingly, a study showed that custodial fathers are less likely to get paid child support by mothers than custodial mothers are to get paid child support by non-custodial fathers. One key factor in that finding is that women after divorce are likely to earn less on average, and thus find paying child support to be more of an economic hardship. Child custody and child support issues are very intertwined and will continue to affect parents who don't live together
Source: Deseret News National, "What America's child support problem is really about" JJ Feinauer, Mar. 06, 2015