NC for this as I think I'm just having a wobble this weekend.
I've never in my life been 100% sure that I want kids. I've varied between 50% and 99.9% for the most part. It seems like too enormous a decision to have no doubts whatsoever about so I'm ok with that.
I spent a lot of my early 30s single and trying hard to convince myself and others that I absolutely DID NOT want them, largely to cushion myself from the fact it might not happen anyway, and to silence those who helpfully reminded me the clock was ticking 
Then I met my amazing DP, fell madly in love and the possibility appeared. We stopped using contraception coming up a year ago now but still no sign. We're both late 30s.
The last few days I've been having a wobble. Reading a lot on here about how hard it is with kids, people who regret it, people having a really tough time etc. Worrying about the potential for disabilities or illness that would make it all very much harder. Thinking of the easy, selfish, lazy days we're having this bank holiday and imagining a difficult baby or hyperactive child or petulant teen in the mix (note that my brain will not let me paint a lovely easy child into this picture).
I think/hope that this is a subconscious reaction to it not being as easy / quick as we hoped. Like again I'm preparing myself for the fact it might not happen for us by focusing all my energy on building up the cons we'd 'escape' so that I've no head space left to mourn the lack of all the pros we'd miss out on.
So, if you're still reading this (and well done if you are) please would you tell me the one thing that makes it all worthwhile? What makes the tears and stress and tantrums and lack of sleep worth it? What moment of the day or week or year makes you grateful for your children?