When you have your first baby, you are stressed. ALL the time! Stressed about food and diapers and clothes and blankets and bottles and Binky's and sleep and... well... everything really. There is no time to enjoy the baby because you don't know that nothing is wrong, that there is no reason to worry. You don't love the first baby less, you just worry yourself into a state of panic about the little things, and then the big things feel like mountains.
With the second child, you are overwhelmed. It is a real challenge to learn how to accommodate a new human being while still providing all the love and attention that the first child needs. You don't worry quite as much, but probably only because you don't have time to. The adjustment to child number 2 is one of the hardest things you will ever do, and still you love them endlessly.
Child 3 is bliss. You have worked out all of the worry and stress on the first child. You already know how to multi-task thanks to child #2. You've been "there" before and been through everything along this road. Or maybe you hit a rough patch but you know how to get the help you need and still deal. With child 3 you can finally enjoy every minute. Not just the perfect minutes, but all the minutes. You might even enjoy the crying minutes and the smelly minutes and the messy minutes, because you know that you will make it through and this little person will be a blessing in your life for a long time. And that makes you love the ride more than you ever imagined you could.
Or at least that's how it is for me.