If you were Chinese and lives in the mainland, then yes neither are avoidable. Eventually your parents would look for someone to have you arranged and have you doing the whole marriage business faster than you can spell the word divorce. But seeing as most of you don't then you pretty much have a say about it, you can choose. Just like the American way I was told by many foreign friends, "There's always a choice."
In my opinion, yes you can avoid marriage and probably even children but it has always bothered me that this way of thinking of avoidance only means that you haven't found the right person. Judge me for saying that but that's what I really think of when I meet someone in their 30s and still has no plan about marriage and/or children. Maybe it's just because of the way I was raised - the all-so-conservative - idea of family, but that's just how I see it.
Wouldn't you get lonely when you're old and there's no one their to keep you warm or even be their just for the sake of companionship?