If we are honest with ourselves, even though we do not want our children to be selfish, they can be selfish. But, if I can be a little more honest, we all are. We all, at times, look for ways to get our wants. We know the benefits of living for others, but there are times when we, like children, live for ourselves.
Since the beginning of time, humankind has been selfish. From the beginning with Adam and Eve wanting to wisdom (Genesis 3:6), and will continue until the new Earth comes.
To rid selfishness, we must be mature.
One key aspect of maturity is to have the ability of delaying gratification. For example, you save money to buy a boat instead of going out and buying on credit.
In parenting, it would be the idea of us delaying personal time for later and being able to be sacrifice time with our children when they are awake. Does any grow man want to play tea time with their daughter? No, but we do because we are trying to be unselfish. Will we fail, at times yes, but we should always be striving to be godly.
The more we practice unselfishness and become more self-sacrificing, the more we are showing our children God because He is the ultimate example of unselfishness.