I think kids are terrific. I love being around them -- I love the way they think, their creativity and imagination. I think they are fun. I prefer older kids and pre-teens, but little kids are okay, too. They are so much less judgmental than adults. This is the main reason I went into teaching/tutoring, so that I could spend time with kids. (Too bad it turns out the politics and other adults aren't worth it.) I think kids are the best -- as long as they aren't mine.
It comes down to this: I love kids. Other people's kids. My husband feels the same way. We like to play with our friends' kids. We think our nephews (ages 6, 5, and 2) are awesome. But I have absolutely no desire for spawn of my own, and neither does my husband. I have no maternal instinct and he has no paternal instinct. So while we enjoy kids, we'd be rotten, miserable, resentful parents. After all, if it's someone else's kid, you get to give it back when you're sick of it.
I tell people my biological clock is set to "dog," because I absolutely dote on my Welsh Corgi, Ein! Clearly I have some level of nurturing instincts. They're just all for dogs and not for babies.