Unpardonable sins

In the Baha'i Writings it is said that not educating ones' children is a "sin unpardonable." After some thought about this, and based on the idea of "repentance" used in the Writings, I believe this is because a person does not have a chance to fix that mistake within ones' lifetime: you can only raise children once. You can fix a relationship with a person and other mistakes in your life, thereby proving your sincere change, but we don't have the opportunity to re-raise children, among other things. This would not mean that you would not get another chance in the life after this one, simply that you couldn't fix it in preparation for that next life.