The Texas legislature is taking up what should be a significant rewrite of the family code this issue. The main driver of this will be the now constitutionality of same sex marriage.
For example is this bill, which shows the many ways this will affect the common law marriage statute, civil unions and the standard possession order.
http://www.capitol.state.tx.us/Search/DocViewer.aspx?ID=85RHB016631B&QueryText=%22child+support%22&DocType=B
This site changes frequently so this link may not be active. I will publish a longer post later in the Spring once we see which of the many proposed amendments to the Family Code become law.