I think your worry is a very common and natural one.
There are a LOT of horror stories out there about the teenage years.
I, for one, don't believe for a single second that it's a foregone conclusion that teens have to be difficult or that their relationships with their parents have to suffer.
In fact, I think it's awesome that you're asking this question while your children are you because you are in a perfect position to lay the groundwork for excellent communication down the road.
Yes, your relationship with your children is going to change as they get older. They are not going to need you for the same kinds of things they need you for now. They are going to want - demand, even - independence. This is normal and necessary to prepare them for adulthood! They will still need you, but in different ways. They're going to need you to be an excellent listener, they're going to need your support when they have trouble with their friendships, they're going to need to to sit in the bleachers and cheer them on at sporting events, they're going to need you to help them with job applications and college searches, they're going to need you to help them expand their minds with intellectual conversation and abstract discourse.
My kids are 12, 10, 10 & 8 and the older kids are getting really, really cool! I love the conversations I have with them now! We talk about science and politics and philosophy. They are developing their own interests in sports and music and drama and it's really fun to watch them cutting their own trails.
So, lay the groundwork now. Talk to them - on their level - about the things that are important to you. Emphasize the importance of open communication and show them - in an age-appropriate way - that you trust in their independence. It's never to early to start talking to your kids about sex, drugs, smoking, healthy relationships, empathy, etc. We've been talking about all of these things since the kids were very little and now, as these issues actually start to become real, there's no "awkwardness" in our conversations.
I can't emphasize enough how important it is to instill a sense of empathy
in your young children and nurture it vigilantly throughout their entire childhoods. Adolescents, by nature, are fairly self-centered creatures, and I've found that by having that solid value of empathy under their belts, "reasoning" with my kids about seeing other people's points of view is much easier. Does that make sense?
Don't worry Mama! Teenagers are great!
: You're going to have a wonderful time with them!