By the way, on the flip side of this (sort of), I've noticed a pattern of gloomy responses I've experienced for whenever life is going well. To wit:

"I'm really enjoying the freedom of single life." Response: "Enjoy it while it lasts. Your life is over once you get married."

"I'm really enjoying married life." Response: "Enjoy it while it lasts. Your life is over once you have kids."

"I'm really enjoying having a child." Response: "Enjoy it while it lasts. Your life is over once you have two."

"I'm really enjoying having two children." Response: "Enjoy it while it lasts. Your life is over once they hit teenage years."

"I'm really enjoying having teenage children." Response: "Enjoy it while it lasts. Your life is over once they leave home."

I kid you not. I have been told variations of all the above, and that last one is the most recent. Sadly, whilst none of the other statements proved true (despite the challenges faced at each stage, alongside the joy), I suspect my wife and I will be devastated when our two leave the nest (our oldest, who is 17, I suspect will do so as soon as he can, given his determination to be independent).

Anyway, great rant, and as Arpad said, it does change as they get older (earlier than 12, I'd say, but obviously everyone's experience is different). :)