Afeta v. Gonzales, 467 F.3d 402 (4th Cir. Oct. 26, 2006) (rejecting derivative citizenship claim that Ethiopian national automatically became a citizen as a minor when his mother was naturalized; "separation agreement" obtained when parents separated was not a "formal judicial document" and therefore did not suffice to show legal separation prior to divorce). See also, Matter of H, 3 I. & N. Dec. 742 (BIA 1949); Brissett v. Ashcroft, 363 F.3d 130 (2d Cir. 2004) (judicial order requiring payment of child support sufficient); Simpson v. T.D. Williamson, Inc., 414 F.3d 1203 (10th Cir. 2005).
http://caselaw.lp.findlaw.com/data2/circs/4th/051174p.pdf