Almost a third of migrants whose ages were disputed under the UK-France "one in, one out" small-boat returns deal have turned out to be children, according to a critical letter sent to a British government minister. Of 304 age-disputed cases recorded between August 2025 and May 2026, 94 were ultimately found to be minors — despite the scheme being designed to exclude children from detention. The letter, written by the interim chair of the Independent Monitoring Boards (the official bodies that scrutinise UK prisons and immigration detention facilities), also flagged detainees being held far beyond the scheme's intended 28-day limit, people facing removal while seriously ill, and families being separated — raising broad concerns about the treatment of vulnerable individuals under the bilateral agreement.