A birth certificate establishes a child's legal identity and is the sole official proof of a child's age. However, quantitative estimates on the economic significance of birth registration are lacking. Birth registration laws were enacted by the majority of U.S. states in late 19th and early 20th centuries. Controlling for state of birth and cohort effects, the differential timing of birth registration laws across US states is used to identify whether birth registration changed the effectiveness of child labor legislation between 1910 and 1930. The incidence of child labor declined significantly in the early 20th century. The study finds that if a birth registration law had been enacted by the time a child was born, the effectiveness of minimum working age legislation in prohibiting under-aged employment more than doubled. This effect was stronger for children residing in non-agricultural areas.This is in line with what I learned from a little research, conducted for my 2007 exam in American Legal History, on the administration of the Keating-Owen Act between its passage in 1916 and its demise in Hammer v. Dagenhart (U.S. 1918). To quote from the exam:
A second issue was what evidence to accept in certifying the age of the child. The states were only just beginning to require the official registration of births; in North Carolina, where many children labored in textile mills, fewer than one percent of births were registered. After conducting public hearings of employers and state officials, a regulation was adopted that declared birth certificates the most reliable evidence, followed (in descending order of reliability) by baptismal records, Bibles regularly used to record a family’s vital statistics, and affidavits from two doctors, one of whom had to be a member of the U.S. Public Health Service. (Employers unsuccessfully attempted to add the affidavits of parents to the list.)In general, the administration of the Act by the Child Labor Division of the Children's Bureau of the Department of Labor struck me as an interesting, if of course truncated, episode in the history of the American state. The Division's director, the Chicago social worker Grace Abbott, struggled to develop procedures that maximized the reach of her small staff without falling violating doctrines of doctrines of administrative law and procedure that were only just taking shape. (Among Abbott's legal advisers were two allies from Chicago's reform movement, Ernst Freund and--wait for it--Roscoe Pound.) A nice master's thesis or dissertation chapter could be written by someone with the requisite legal and historical skills and access to the National Archives.