Kids who don't get enough sleep may be more likely to become obese later in life, according to a new study from the University of Washington.

Data was collected from nearly 2,000 children and compared those who slept at least 10 hours a night with those who slept less. The weight of the children were closely monitored over a five-year period.

"(Infants and toddlers) were nearly twice as likely to move from normal weight to overweight, or overweight to obese in that five-year period," said Janice Bell, child health researcher for the University of Washington.

Doctors said it is very important for children under the age of five to get at least 10 hours of sleep at night. Infants and toddlers should acquire between 11 to 15 hours.

However, napping in the daytime is not a substitute for lack of nighttime sleep. Researchers think nighttime sleep affects how the brain regulates tiredness and metabolism.

"We found that their napping didn't have any effect on their later obesity, whereas the nighttime sleep was significant," Bell said.

Children who are tired are not as physically active and that leads to a tendency to gain weight.