Unwed parents are becoming more common - some estimates are that more children will be born out of wedlock than in it by 2016. Unwed parents may eventually get married, though perhaps not to the person they first had children with.

In recent times, unwed parents are assumed most receptive to marriage right after a baby's birth, a period dubbed the "magic moment."  But that doesn't seem to be the case, according to a paper from Duke University sociologist Christina Gibson-Davis. Davis says the best window of opportunity for a union seems to be before the child turns 3, though patterns vary greatly by race, with more African-American mothers marrying much later than mothers of other races or ethnicities. 

The conclusions drew upon a nationally representative survey that looked at 5,255 U.S. children born out of wedlock. 

"It turns out the 'magic moment' lasts longer than conventional wisdom has held," said Gibson-Davis. "And for some subgroups, that moment lasts even longer."

The study found that most children born out of wedlock don't remain so: 64 percent of children born out of wedlock see their moms get married, though many of those marriages don't last. Nearly half of post-conception marriages end in divorce, and those numbers are higher still for African-American women.

"These marriages are fragile," Gibson-Davis said. "If you think that stable marriage is beneficial for kids, very few kids born out of wedlock are experiencing that."

The odds improve somewhat when mothers marry their child's biological father, Gibson-Davis said. After 10 years, 38 percent of post-conception marriages involving biological parents had dissolved. In the same period of time, 54 percent of marriages to a stepfather had ended. Those findings held true across racial lines.  

Despite years of public attention to children born out of wedlock, big gaps remain in our picture of how these children actually live, Gibson-Davis said. "Those who would promote marriage have more work to do."