"Sally the Witch" ("Mahōtsukai Sally") and "Himitsu no Akko-chan" are both pioneering series in the magical girl genre, but they have distinct release timelines:
Sally the Witch: This series was the first magical girl anime. It originally aired from December 5, 1966, to December 30, 1968. This makes it an early trailblazer in the genre, bringing the magical girl concept to anime television source.
Himitsu no Akko-chan: Although the manga for "Himitsu no Akko-chan" was serialized earlier, from 1962 to 1965, the anime adaptation came out later than "Sally the Witch," beginning its television run in 1969. This establishes its anime as following in the same genre footsteps created by "Sally the Witch" source.
Therefore, while "Himitsu no Akko-chan" may have been among the earliest manga of its kind, "Sally the Witch" holds the title of the first magical girl anime.