Mothers should be very careful at the amount of sleep their newborn babies are getting, according to a new study published Monday, which found that infants who sleep an average of less than 12 hours per day may have an increased risk of being overweight in early childhood.

Researchers at Harvard Medical School recorded the sleep habits of 915 children at ages 6 months, 1 year and 2 years, using questionnaires and in-person interviews. At each visit, they recorded the infants’ length and weight and had parents report on the number of hours their children watched television or videos.

The study concluded that the more sleep infants got, the less likely they were to be overweight at age 3. Babies who slept for less than 12 hours a day were twice as likely to be overweight compared with children who slept more. Those who slept less than 12 hours per day and watched 2 hours or more of TV per day were 6 times more likely to be overweight.

According to the study, more than a third of children aged under four have a TV in their bedroom and experts have warned that a quarter of youngsters will be clinically obese by 2050 unless action is taken.

“Mounting research suggests that decreased sleep time may be more hazardous to our health than we imagined. We are now learning that those hazardous effects are true even for young infants,” Dr. Elsie Taveras, assistant professor in Harvard Medical School’s Department of Ambulatory Care and Prevention and lead author of the study said, according to BBC News.

“Getting enough sleep is becoming more and more difficult with TV, internet and video games in the rooms where children sleep. Our findings suggest that parents may wish to employ proven sleep hygiene techniques, such as removing TVs from bedrooms, to improve sleep quality and perhaps sleep duration,” Dr. Taveras added.

The study – the first to report an association between infant sleep time and children’s being overweight - was published in the Archives of Pediatrics and Adolescent Medicine.