But if one or either of the ten virgins, after she is espoused, shall be with another man, she has committed adultery, and shall be destroyed; for they are given unto him to multiply and replenish the earth, according to my commandment, and to fulfil the promise which was given by my Father before the foundation of the world, and for their exaltation in the eternal worlds, that they may bear the souls of men; for herein is the work of my Father continued, that he may be glorified.

Joseph Smith, Doctrine & Covenants 132:63
https://www.churchofjesuschrist.org/study/scriptures/dc-testament/dc/132.p63#p63

The youngest was Helen Mar Kimball, daughter of Joseph’s close friends Heber C. and Vilate Murray Kimball, who was sealed to Joseph several months before her 15th birthday.

Plural Marriage in Kirtland and Nauvoo, Gospel Topic Essay
https://www.churchofjesuschrist.org/study/manual/gospel-topics-essays/plural-marriage-in-kirtland-and-nauvoo?lang=eng