The importance of forgiveness can be taught with a fuse and a breaker box.
You will need a fuse (preferably on old fashion home fuse box fuse) and access to a breaker box.
Start by "introducing" the kids to the fuse. I gave the fuse the name Bob just to make it fun. Show how a fuse has a wire that will melt a power surge hits which turns off the electricity current. The power surge represents something that someone does that hurts or offends you.
When Bob is offended he blows up and never forgives. because he never forgives he is useless. He is bound for the trash can.
Second, show the kids the breaker box (My kids named it Tom). Explain how the breaker trips when a power surge goes through it but it can be reset and continue to work.
Because he can forgive Tom is able to continue to be useful and go on functioning as he's supposed to.
When we have been hurt or offended we can choose to blow up and refuse to forgive like Bob or we can choose to forgive and go on like Tom.
Tom is acting like Jesus when he forgives. Psalm 86:5, TLB. "O Lord, you are so good and kind, so ready to forgive; so full of mercy for all who ask your aid."
Jesus says we need to forgive if we want to be forgiven by God. Matthew 6:14-15, TLB. "Your heavenly Father will forgive you if you forgive those who sin against you; but if you refuse to forgive them, He will not forgive you."
We forgive because Jesus forgave us. Ephesians 4:32, NIV. "Be kind and compassionate to one another, forgiving each other, just as in Christ God forgave you."