Most parents can tell if their child is not getting enough sleep. My four year-old son is an angel when he is well rested, but when he is behind on sleep... watch out! Here are some average times that most kids sleep.

1 week	16.5 hrs
1 month	15.5 hrs
3 months	15 hrs
6 months	14.25 hrs
12 months	13.75 hrs
2 years	13 hrs
4 years	11-12 hrs
5 years	11 hrs
10 years	9.75 hrs
Adolescent	7.5 hrs (school night)
Adolescent	8.75 hrs (weekend)

Some kids will sleep more or less than this. The important thing is that your child feels and acts well rested.