Generational curses starts with God cursing Adam and Eve in Genesis 3:17. Another instance includes Exodus 20:5 in which God warns the Israelites against idol worship, which attracts a curse up to the third and fourth generations. The same warning is recorded in Deuteronomy 5:9.
Genesis 9:18-29 records the story of Noah and his family. When Ham, the youngest son, sees his father's nakedness and makes fun of it, Noah curses him and his lineage, Canaan. Shem and Japheth are blessed for covering their father's nakedness.
Exodus 34:6-7 describes God's mercy as forgiving iniquity and transgression even though he does not let the guilty and their children go unpunished, to the third and fourth generations. Later in Deuteronomy 23:2, Moses tells the Israelites that children born out of wedlock are cursed to the 10th generation.
1 Samuel 3:12-14 portrays the curse on Eli and his family brought about by his sons for defiling the temple. They sin against God by seducing and committing sexual sin with the young women who assist at the entrance of the Tabernacle, yet Eli fails to discipline them. God through his messenger warns that no amount of sacrifice, offering or atonement can cleanse Eli's lineage.
In Jeremiah 31:29-31 and Ezekiel 18:1-4, 14-20 a new covenant is ushered, stating that the son is not punished for his father's sin. Jeremiah 31:30 states that, henceforth, everyone must answer for their own iniquities against God. Jesus' sacrifice heralds the coming of the new covenant in Luke 22:20.