How do I get my baby to sleep longer in the night?

My first was up 3-4 times a night, my 3rd slept 6 hour stretches from the night he was born. Babies at different ages average different amounts of sleep, and if you are unwilling to shorten the naps he has during the day, as I found I had to do with my oldest child, then I don't have any other suggestions for you. Sorry. :(