As of February 25, 2026, a child cannot travel to the UK without a valid passport (or a specific Certificate of Entitlement), even if they are a British citizen. New "Permission to Travel" regulations and the full enforcement of the Electronic Travel Authorization (ETA) system mean that airlines are strictly prohibited from boarding any passenger, regardless of age, who does not possess an approved travel document. Previously, some children could travel between Ireland and the UK on a birth certificate, but as of late February 2026, even British and Irish nationals on these routes must present a valid passport or Irish Passport Card. For non-British/Irish children, an ETA (costing £16) is required in addition to their passport. There is no longer any provision for children to "ride" on a parent's passport. If a child's passport is lost or expired, parents must secure an "Emergency Travel Document" from a consulate. This policy is part of a broader UK initiative to ensure that every individual crossing the border has a digital record and a verified identity before they even arrive at the gate.