The study included 519 healthy 7-year-olds from New Zealand, who each wore a device called an actigraph for 24 hours. An actigraph records movement, providing an objective measure of a child's activity level and sleep time. Parents also noted when their child went to bed, which allowed researchers to calculate how long after bedtime children actually fell asleep.Active days mean better bedtimes (via Consumerist)
The researchers found a wide variation in how quickly children fell asleep, with some taking as little as 13 minutes and others needing more than 40 minutes after going to bed. Within this range, there was a close relationship between the onset of sleep and daytime activity. On average, children took an extra three minutes to fall asleep for every hour they weren't moving about. Also, the children who fell asleep faster slept longer overall. On average, children got one extra hour of slumber for every 11-minute drop in how long they took to get to sleep.