Children should get at least eight hours of sleep at night. A little more is good for younger children but the minimum amount should be eight hours. Teenagers will try to get by with less, ( stay up later) but they need at least 7 hours to function properly.
Most young children require 12 to 15 hours of sleep a day in order to function properly in every day life. This will reduce tantrums and fussy children.
It does depend on the age of the child (and remember, not all children are the same), and it also depends on if they nap, but generally, children should get between 10-12 hours sleep a night.