One major theme runs through the bible from cover to cover: forgiveness. The lives of biblical people were lived as an example for us to follow, learn from, and teach to our children. There are both minor acts of forgiveness required and major events that all of us, and our children, are confronted with during our walk to heaven.
Minor events, requiring forgiveness, happen on a daily basis, and offer parents a chance to teach. However, the hardest part is being consistent during these opportunities. Daily occurrences, such as a child “borrowing” something from the other or something as ghastly as breaking said property, offer the most opportunity. Teaching accountability is required here, but ultimately forgiveness is what keeps their relationship together, and allows them to grow closer in the end. See Mark 11:26 and Luke 17:4 among many others.
Then there are life-changing events that seem to be the norm in our society today. Most churches now teach that divorce is acceptable to God, sighting Deuteronomy chapter 24, though later He explains it was because of the hardness of heart that divorce was granted (Mark 10:5, Matthew 19:8). God wants husbands and wives to stay together (Mark 10:6-9). God hates divorce (Malachi 2:16).
The level of forgiveness is to equal that which God gives to us (Ephesians 4:32, Colossians 3:13). The death of Jesus raised the bar for us to meet, and to show in our daily walk with Him. Forgiveness should be taught from simple acts on a daily basis, and mammoth sized life challenges that confront families.
Children learn from example. Whether parents forgive little things that happen on a daily basis or life changing incidents, children are watching and learning. Parents can preach and teach all they want, but children learn through patterns and behaviors of their parents.