Alma 23

The Lord has said many times in scripture -

"...I the Lord thy God am a jealous God, visiting the iniquities of the fathers upon the children, unto the third and fourth generations of them that hate me..." (Book of Mormon | Mosiah 13:13)

As well as -

"...thou shalt be rewarded for thy righteousness; and also thy children and thy children's children unto the third and fourth generation." (Doctrine and Covenants | Section 98:30)

It basically becomes clear that the impact of the faithful or wickedness of parents will have its impact on future generations. We learn as the word was preached to the Lamanites, that Mormon comments -

"...as many of the Lamanites as believed in their preaching, and were converted unto the Lord, never did fall away.
7 For they became a righteous people..." (Book of Mormon | Alma 23:6 - 7)

As we continue reading the Book of Mormon, we learn that this righteousness continued through many generations. At the same time we find the Amalekites and Amulonites were Nephi apostates. As a result, we now find a generation or two later, unrighteous and wicked posterity. We know nothing of the Amalekites but we do know the Amulonites were descendants of Amulon, one of the wicked priests of Noah, that kidnapped Lamanite women to be their wives. Of this people, as the sons of Mosiah preached among them -

"...the Amalekites were not converted, save only one; neither were any of the Amulonites; but they did harden their hearts..." (Book of Mormon | Alma 23:14)

No wonder the Lord has said -

"...inasmuch as parents have children in Zion, or in any of her stakes which are organized, that teach them not to understand the doctrine of repentance, faith in Christ the Son of the living God, and of baptism and the gift of the Holy Ghost by the laying on of the hands, when eight years old, the sin be upon the heads of the parents." (Doctrine and Covenants | Section 68:25)