The binding principles established are: (1) Parental custodial rights acquired by operation of law under the law of a child's habitual residence at birth (Italy) subsist after a change of habitual residence to another state (Switzerland) pursuant to Article 16(3) of the 1996 Hague Convention and do not require re-registration. (2) The habitual residence of a young child is determined by the dependency model - the child acquires the habitual residence of the custodial parents. (3) "Habitual residence" requires an objective assessment of where the child's actual center of life was located, based on the duration of stay, relationships established, and settled purpose of the parents (particularly employment), not on subjective intentions about permanence or conditional factors like marriage plans. (4) Under Article 3 of the 1980 Hague Convention, retention is wrongful if: (a) it breaches custodial rights under the law of the state of habitual residence; and (b) those rights were being exercised at the time of retention. Both elements were established on these facts. (5) Acquiescence under Article 13(a) requires clear evidence that the requesting parent, with knowledge of rights, consented to or acquiesced in the retention. Merely exercising court-ordered contact rights does not constitute acquiescence. (6) In the absence of expert evidence and where the child has successfully spent time with the requesting parent, allegations of mental health issues do not establish "grave risk of harm" under Article 13(b). (7) Delays in proceedings and the child settling in the new environment cannot reward the wrongful retention or defeat a return order, as this would subvert the Convention's aims. (8) Courts in Hague Convention applications conduct only a summary, short-term best interests inquiry focused on prompt return, not a full merits determination of custody, which is reserved for courts of the habitual residence.