The family is a microcosm of society. People learn to act responsibly, to consider others, to accept authority, to have loyalty, and to attend to the members who need care and protection. Instilling values on the family level ensures that such values are intrinsic to a society.
I will say that our children should be the most important people in our lives. Too many times parents have children and act as if their lives shouldn't change. Decisions should be made in terms of what is best for the children. This is not always the easy or popular decision, but this leads children to become stronger, healthier, and happier children.
Families are very important and most definitely have an impact on the way we grow up and who we become as adults. For me personally, my family is very important to me. With this being said, not everyone has a traditional family structure. Some kids grow up with wonderful families while others are raised being abused and mistreated by their families. I think the answer to your question is really dependent on the individual.
I think it depends on how you define most important. as stated above the role your family plays in your life may change as you grow and change, however the importance of family is still there, maybe just on a different level.
I think that this is generally true, but not in all cases.
Our family is definitely the most important group of people in our lives as we grow up. They give us our basic education -- both academic (to some extent) and social. They teach us lots of things that we need to know for school, but they also teach us how to behave.
Later in life, our families become less immediately important. They do not influence us as much on a day to day basis. So we can say they are no longer the most important people. However, they still have a huge impact on us because they have sort of created the foundation that has made us into the people we are. So even though they do not impact our decisions and such directly, the things they taught us early on continue to have a huge impact.