From the time a baby is born until he is about six months old, he requires more sleep than an adult — a lot more. Newborns may sleep between 12 and 18 hours out of every 24-hour period. After a child is about six months old, his sleep requirements are a bit higher, but very similar to an adult’s sleep requirements.
It is of the utmost importance that parents help the child to establish a regular sleep/wake schedule as early as possible. This will make life easier for everybody in the household, including the baby. Babies, even as young as six months old, like continuity.
A regular “go-to-bed” time and a regular “get-up” time as well as a regular “naptime” will help to prevent all kinds of sleep-related problems.
There are lots of reasons why children can have sleep problems. Some of the problems are caused by physical discomfort or illness. Some sleep problems are caused by emotional or developmental problems that might seem totally unrelated to sleep. If your child is consistently unable to sleep (and consistently is the operative word here) it is best to talk to your pediatrician about the problem and have him or her help you resolve the issue.
The thing to remember is that when humans are tired, no matter how old or young they are, they sleep if they aren’t having mental, physical, or emotional pain. Sleep is natural; it isn’t a behavior that must be learned.
If you have worked to establish a regular schedule for your child (eliminated all of the foods and drinks that might prevent sleep, read him a story and tucked him in), and sleep continues to be a problem, it really is time to seek professional help. The lack of normal sleep is a symptom, not a disease.