I was reading an article on Dr. Weil today about this and then saw the National Sleep Foundation has a list of how many hours children need. You can find it here:
When my daughter was 3 months old, she was sleeping 12 hours every night and then 2-3 hours of naps throughout the day. I did something similar to the Ferber method and it taught her to self-soothe to return to sleep and not be dependent on us to fall back asleep. It worked within 5 days and from then on, she never has had sleep problems and didn't cry when I put her in the crib at bedtime and she didn't wake up during the night crying. She also didn't get sick at all until she was 2 years old. I contribute that to her getting enough sleep every night. When a lot of other parents were having sick babies and dealing with ear infections and babies up at all hours of the night, I wasn't. Looking back now, I really believe it was mostly because she was getting the sleep she needed.
Naps generally are not needed for children from age 4 and on and that is about the time Katie stopped needing naps as well. She continued to sleep 12 hours a night until she was about 5 and now only needs 10-11 hours of sleep a night, which is the recommended sleep for children ages 5-12.
If you have a child with learning or behavioral problems or is sickly more than average, first look at how much sleep they are getting. It does make a difference!