Some handbooks and textbooks recommend that each other be restricted to reference to two and one another to reference to three or more. The distinction, while neat, is not observed in actual usage. Each other and one another are used interchangeably by good writers and have been since at least the 16th century.
First Known Use of ONE ANOTHER
ONE ANOTHER Defined for Kids
Definition of ONE ANOTHER for Kids
:each other<They looked at one another and laughed.>