WoWDB

Peanut, Willy, and Egbert are possible quest rewards from the same quest, which can only be completed once for  Children's Week . It will take you three years to earn this achievement because of the one-character restriction. This cannot be circumvented by learning it from its battle pet form - it must be learned from the item which actually "teaches" you the pet as described in the achievement tooltip.

The achievement is not part of the Children's Week meta-achievement,  For the Children.