Every child born in the Altona district of Hamburg receives a Danish passport
Okay, we cheated this time. Not entirely, though. Altona has only been part of Germany since 1937. The former fishing settlement, although part of the Duchy of Holstein, was administered by Denmark until the end of the Second Schleswig War in 1864. From 1664 then, when it was granted city status and customs exemption, Altona was the second-largest Danish city, outstripped only by Copenhagen, competing with neighbouring Hamburg. But babies born in Altona are, of course, genuine children of Hamburg, and Danish is not normally offered as a foreign language in the schools of the borough.
There are still plenty of links to our northern neighbour, though, and our catchment area stretches across the border into southern Denmark.