In Whallon v. Lynn, 230 F.3d 450 (1st Cir. (Mass.) 2000), the Court of Appeals held that the father had "rights of custody" under Mexican law, which was law of her habitual residence at time of her removal, as the doctrine of patria potestas gave the father custodial rights greater than mere visitation rights, notwithstanding the Mexican court's rejection of father's petition to terminate the mother's parental rights. The Affidavit of a Mexican attorney indicating that both parents exercise patria potestas rights under Mexican law and stating that both parents must consent to the removal of the child under Mexican law was an acceptable form of proof in determining issues of foreign law, and was permitted under the Hague Convention.

The child's return to Mexico would not subject child to grave risk of physical or psychological harm or otherwise intolerable situation, notwithstanding alleged instances of verbal and physical abuse committed by father, who resided in Mexico, as none of abusive conduct was directed at the child. An opposing return must establish that the alleged physical or psychological harm is a great deal more than minimal; the harm must be something greater than would normally be expected on taking a child away from one parent and passing him or her to another, and courts are not to engage in a custody determination or to address such questions as who would be the better parent in the long run. The father did not acquiesce the mother's removal of the child from Mexico, even though he did not institute formal custody proceedings and wrote a note allegedly acknowledging that the mother could relocate with the child, in light of the father's subsequent increasing involvement in child's life, and the father's prompt and persistent actions seeking the child's return to Mexico following her removal.