Key points are not available for this paper at this time.
John Boli-Bennett, John W. Meyer, The Ideology of Childhood and the State: Rules Distinguishing Children in National Constitutions, 1870-1970, American Sociological Review, Vol. 43, No. 6 (Dec., 1978), pp. 797-812
Boli-Bennett et al. (1978) studied this question.