Sleep quantity needs vary based on age. But common "rules" about how many hours of sleep an infant or a 2-year-old need might not be helpful when it comes to your own child. These numbers are simply averages reported for large groups of kids of particular ages.
There's no magical number of hours all kids need in a certain age group. Two-year-old Lilly might sleep for 12 hours, while 2-year-old Marcus is just as alert the next day after sleeping for only 9 hours.
Still, sleep is very important to kids' well-being. The link between a lack of sleep and a child's behavior isn't always obvious. When adults are tired, they can be grumpy or lack energy, but kids can become hyper, disagreeable, and have extreme changes in behavior.