More girls under 15 give birth in Houston than any other U.S. city, according to a new national report, and many of the city's teen moms have additional children before they turn 20. The report by the research organization Child Trends found that there were 20 percent more babies born to girls 14 or younger in Houston than in New York and Los Angeles in 2006 and that 24 percent of all Houston's teen births were repeat births that year, the latest for which data is available.