I remember when our third child was finally out of diapers - this was an enormous milestone. I called my mother and said, "Mom! I'm finally over the worst!" Wise woman that she is, my mother simply laughed. I guess that was my first clue that there would be plenty more challenges before my children were raised. And there certainly were. But what I really didn't understand was that even when your children are grown and have children of their own, you still suffer when they have hard times and thrill when they are happy. Being a parent doesn't end when they get married or move out of the house.
It is important, of course, to stand back and let your kids become independent. It is a good idea to start working on this concept while they are still in their teens. Making their own decisions (and sometimes suffering the consequences) is a big part of learning how to survive on their own.
A wonderful thing happens when your children learn all that it means to fend for themselves, and especially when they have children of their own: they come to appreciate all that was involved in bringing them to their present state. This is when (finally!) true respect is born and you begin a new kind of relationship with them. It becomes more of a give and take, rather than the one sided give, give, give. This is when advice is asked for, and actually followed! This is when your knowledge (of recipes, sewing skills, gardening tricks, etc.) is sought out and transferred. And this is a time when, if you are very lucky, your children seek out your company because they just plain like you.
This is the stuff that makes growing older worth it: the ultimate joy of having grandchildren around and the pure pleasure of the transformation of your children into your friends.