Do I really want kids? What would you do?

I'm late 20s and my boyfriend is the same age - been together 6 years. During our relationship, I always knew he wanted kids and I did too (or at least thought so). I was never overly excited about having children (not so much the taking care of them part, but the pregnancy and birthing part), but I figured I would come around as I've always envisioned them in my future. WELL, now that we're getting older and the relationship may be going to the next level, I'm still not overly thrilled about the prospects of children. I feel like I can see them in my future, but in reality, I have zero interest in getting pregnant right now or maybe even in the next few years (if we were married) which is a problem for the whole biological clock thing AND taking things to the next level. The whole real spin on how my life would change and how much work it would be (and I wouldn't call myself lazy) is very unappealing. I just don't know what to do. He wants me to promise to him that I want to have 2 children to take the next step, but I've never been a timetable type of person. I don't like setting time tables on...i have to be married by x age and pregnant by x age and have this and that by x age. So, I'm freaking out! Has anyone else dealt with this/what advice do you have for me. I would hate for 6 years down the line to really want children and for have given up my relationship with him because I can't promise 2 kids by 35.