It is good for us to have high expectations for our children because it does help them to become better than if we have lower expectations. The thing we have to learn from God's example is that we have to be merciful and gracious. When those little cherubs seem more like little demons we need to remember that they are young (foolishness is bound in the heart of a child - Proverbs 22:15), that we were young once, and that even though we are grown we still are not perfect. I know the struggle we have with wanting our children to be better than we are, but they are going to make mistakes. I remember one young teen who wanted desparately to become a Christian, but his mother, who was a Christian, wouldn't let him. When I asked her about it she explained that he had problems with his mouth and some other issues. In other words, he was not perfect and sinless. She wanted him to repent and straighten up his life and show her that he could live right before letting him be baptized. I asked her about how long she had been a Christian and whether she still said and did things that she shouldn't. She admitted that she had problems in some of these same areas that she wanted him to correct before he could be baptized. If we could straighten out our own lives why would we need a savior? That doesn't mean that this young man doesn't need to repent, but that even Christians are not perfect.
If they become better than we are it will be because we have learned from our mistakes and have taught them to avoid some of the traps that caught us. In addition, it will be because we are open and honest about our imperfections and encourage them to follow others who are stronger in the areas where we are weak. We need to encourage our children to follow us as we follow Christ, and to follow Christ if they see us not following Him in some area.