How long has to sleep a baby?

When our baby has born,to achieve that he(she) sleeps during the whole night is an
important event that we all wish to happen.
Parents usually have lots of questions, more when the baby is recently born or they are
first time parents. 
The first and the most important question is how many ours the baby have to sleep. Every baby is different, so
their sleep is different about other babies. Don’t worry about it, we want to
give you some instructions about the sleep of your baby.
A newborn child usually sleeps about 16 or 20 hours, they don’t distinguish the day of
the night, and when wake up, usually they are hungry .
With three weeks of life, babies sleep about 16 or 18 hours. With six weeks, 15 or 16
hours and they will reduce his sleep hours until arriving at nine months, when
they sleep 10 or 11 hours.
As the babygrows up, they do nap during one or two hours. For this reason with 18 months
our baby will sleep until 13 hours, plus two naps. With three years, will sleep
10 or 11 hours, and will do a nap of two more hours.
 Our childwill need rest to have energy, so they will have to sleep the necessary hours.