The couples I know without children seem to have more money, less stress, smarter homes, good marriages, more (and more exotic) holidays etc. They may look at us and think 'They have it all: cute kids, cosy clutter, fun etc.' More likely they may step over the threshold, glance at each other and think 'Thank god that's not us'. Who knows? You never know what really goes on behind closed doors.
From what I do know, some of our friends wanted to have kids, but couldn't; others chose not to. That probably plays a big part in whether these couples have any 'regrets' about being childfree.
I think I wasn't particularly clucky, but there was an element of 'the path less trodden' - I knew that if I didn't have kids it was an experience I'd never be able to replicate. As it happens, I fell in love with the DC and despite the stress, lack of sleep, negative effect on finances, necessary lack of spontaneity etc., it still somehow seems like a good thing.
As for not really enjoying being with other people's kids - I read once that Kids are like Farts - you can tolerate (or even like!) your own, but other people's... So, your feelings about other people's kids does not necessarily mean you'd be a rubbish parent.
As others have said, at 30, no need to sweat it too much. Do some travelling, persue your career, have uninterrupted nookie at the weekends etc. If you suddenly feel the urge to procreate, I'm sure your ovaries will let you know. If you don't, all the better - put your energies and resources into hedonistic and altruistic activities of your own choosing.