My pregnancy wasn't planned and I felt exactly this way and still sort of do. I felt okay about having a baby but I really wasn't happy about the fact that she would grow up! I've always loved babies but the thought of school-age children or teenagers terrifies me. Don't really have any advice because I am hoping (like others have reassured you above) that it will be different when it is my own and we are growing together but wanted to let you know that you aren't alone! My DD is only 4 weeks old and I still feel anxious about the older stages but I'm just taking it one day at a time and enjoying her as a baby while I can

I think it is normal to have doubts, worries and concerns -- it lets you know you are going to strive for the best and that is kind of reassuring, if you know what I mean!