One in 10 infants and toddlers have problems sleeping at night and may be at greater risk of developing a sleep disorder as they get older, a new study suggests.

The new research is a rare look at a problem that many parents and even pediatricians sometimes fail to notice. The study, which looked at children ages 6 months to 3 years, found that sleep problems were common in this age group. But parents did not always perceive red flags like loud and frequent snoring — which can be a risk factor for obstructive sleep apnea, a potentially serious breathing disorder — as problems that warranted mentioning to their pediatricians.

The findings also challenged a widespread notion that children who have sleep troubles early on tend to outgrow them. In the study, children who had one or more sleep problems at any point in early childhood were three to five times as likely to have a sleep problem later on.

“The data indicate that sleep problems in children are not an isolated phenomenon,” said Dr. Kelly Byars, an associate professor at the Cincinnati Children’s Hospital Medical Center and an author of the study, which was published in the journal Pediatrics. “If you have it early and it’s not remedied, then it’s likely to continue over time.”

The warning signs of a disorder can vary widely. But some indicators of a potential problem in children are loud snoring several nights a week, frequent bouts of getting up in the middle of the night, nightmares or night terrors, and routinely taking longer than 20 minutes to fall asleep.

Although serious sleep issues are more often thought of as a problem of adulthood, the National Sleep Foundation estimates that up to 69 percent of children younger than 11 have a sleep-related problem of some kind. Many parents, though, do not know what to look for or how to distinguish a true sleep disorder from the normal challenges of putting an infant or child to bed.

Pediatricians, too, may also overlook a child’s nighttime troubles. One report found that roughly half of all pediatricians do not ask about or screen for sleep disturbances when talking to parents about the health of a toddler or infant.

For the current study, Dr. Byars and his colleagues followed 359 infants, interviewing their mothers when the children were 6 months old, then again at 1, 2 and 3 years of age. Over all, about 10 percent of the parents reported that their children had problems like night awakenings, restlessness and trouble falling asleep.

Dr. Byars, who sees many children in his practice as a behavioral sleep medicine specialist, said parents often view a child’s difficulties at bedtime as a problem that goes away with age. “We hear that often in the clinic,” he said. “Parents will say, ‘We were told that Johnny or Suzy’s sleep problem was common and that this was just a phase.’ I think that’s true for probably the large majority of kids. But we’re finding that there’s a subset of kids that have a sleep problem that persists over time.”

The researchers, for example, found that up to 35 percent of the children who had trouble sleeping at the start of the study continued having problems over two years later. In comparison, less than 10 percent of the children who did not have sleep issues at the start of the study developed them later on.

Parents also tended to overlook potentially more serious problems. Between 12 and 20 percent of the children in the study snored most nights of the week, a possible sign of obstructive sleep apnea, but most parents did not report it as a problem. Although most children with sleep apnea outgrow it, the condition can result in failure to thrive, poor academic performance and behavior problems in some. The condition can usually be successfully treated with surgery to remove the tonsils and adenoids, or through weight loss and the use of continuous positive airway pressure, or CPAP, machines, which drive air into the lungs.

Dr. Byars said the best way parents can distinguish a true sleep disorder from a phase is to be on the lookout for problems that persist over time, and to raise any concerns with a pediatrician. “If a child has problems across two consecutive well-child visits” — at the 6-month checkup, for example, then again at 12 months, “then that is likely an indicator that this is a problem that should be addressed, as opposed to saying that it’s a problem the child will grow out of,” he said.

“As we say in our clinic, no sleep problem is insignificant if it’s having an impact on the family,” he added.