I feel like this too and I think why oh why didn't I cherish my firstborn more in his babyhood. Not that I didn't cherish him, but I just didn't realise how quickly they grow up.. and that once they do, babyhood is long gone. It's cruel in a way. By the time you're getting enough sleep to really enjoy them, they're growing up and becoming so independent... and then you start to want another, which is easy to contemplate when you're getting a good nights sleep.