You’ve probably noticed your toddler is whinier and more easily frustrated on too little sleep. You may also know that when your little tornado misses a nap, your day can get pretty miserable, too. But lack of sleep is actually hazardous for young kids in surprising ways.

Toddlers need 12 to 14 hours of sleep in each 24-hour day, says Harvey Karp, MD, a pediatrician and assistant professor of pediatrics at the University of Southern California School of Medicine.

Your kid's mood is just one of the more obvious effects of too-little sleep.

“Toddlers with a shortage of sleep tend to be far more irritable and moody than normal,” says Karp, who is author of the book "The Happiest Baby Guide to Great Sleep: Simple Solutions For Kids From Birth to 5 Years." "They’re also more likely to zone out when they should be paying attention, and they alternate between acting unusually sluggish and zooming around the house as if they were hyped up on caffeine.”

Of course, the last part may seem like your urgent, busy little person on a typical day. But sleep studies increasingly caution that chronic lack of sleep in toddlers may undermine your tot's ability to solve problems, and may contribute to behavior and mood disorders in later life.

Related: Block Blue Light and Sleep Better Tonight

Anxiety, worry and negativity

A recent study, published in the Journal of Sleep Research, found that sleep-deprived toddlers were significantly more anxious and worried — two traits the researchers noted were linked to poor performance in school in later years.

In a simple but ingenious study, the researchers compared two groups of toddlers aged 30 to 36 months. Both groups of youngsters went to bed at 8 p.m. and got up at 7 p.m., getting 11 hours of sleep under their belts. But only one group took a 90-minute nap later in the day.

Among other things, the sleep-deprived tots acted less like toddlers and more like tired, grumpy little adults. For example, they showed 31 percent more worry and anxiety when trying to solve an unsolvable puzzle and 34 percent less joy and pride in problem-solving than their well-rested peers.

Related: 8 Ways to Get The Sleep You Need During Pregnancy

Depression

The behavior of the nap-deprived toddlers “mirrors the symptoms of major depressive disorders,” the researchers wrote. In other words, without enough sleep, your happy toddler may show signs of what, in adults, would be called clinical depression.

The study showed that missing a nap “taxes the way toddlers express different feelings …Their coping skills decrease and they may be more prone to tantrums or frustration. Over time this may shape their developing emotional brains and put them at risk for life-long mood-related problems,” researcher Monique LeBourgeois told reporters.

“Many young children today are not getting enough sleep,” she added, “and for toddlers, daytime naps are one way of making sure their ‘sleep tanks’ are set to full each day.”

Aggression

Another report, from Indiana State University, found that two-and-a-half year olds who were active but didn’t get enough sleep were more aggressive than active, well-rested ones. Further research from the same university suggested chronic sleep disruption interfered with tots’ ability to regulate their behavior.

A higher risk of obesity

At a time when so many children are overweight, Karp say it’s worth noting that sleep-deprived kids tend to eat too much food. “They become more impulsive eaters,” he says.

In fact, skimping on sleep in early life may increase the risk of childhood obesity, according to several studies. A study of more than 2,000 youngsters, published in the Archives of Pediatric & Adolescent Medicine, found that children under five who slept less than 10 hours were 80 percent more likely to be obese five years later. In addition, daytime napping did not appear to protect the children from this risk.

Another study, published in Pediatrics, looked at 300 kids between four and 10 and found that the youngsters who got too little sleep both during the week and on the weekends had a four-fold risk of obesity compared with peers who were better rested.

No one is quite sure why sleep affects weight, but Karp speculates that a lack of sleep may slow down children’s metabolism and sap their energy for exercise.

Related: Can’t Lose Weight? Check Your Sleep

Solving the sleep problem

Karp and other researchers suggest a calming, consistent bedtime routine, more outdoor play, talking over bedtime fears, cutting down on screen time and cartoon mayhem and other strategies to help your toddlers get a good night’s sleep every night.

And if your toddler sleep training is harder than you expected, you have lots of company. “Remember that while these scream-filled evenings may seem endless, they’ll be over soon,” he says. “Millions of parents have survived this experience, and so will you.”

Related: Toddler Sleep Training: Goodnight, Room

Chris Woolston, M.S. is a freelance writer and editor who specializes in science, health and travel. A reformed biologist, Woolston says, he studied algae and nitrogen dynamics in Antarctic lakes before the Science Writing Program propelled him out of the lab. He is a contributing editor at Nature.com, a former staff writer for Time Inc.’s Hippocrates magazine, and co-author of Generation Extra Large (Perseus). He lives in Billings, Mt., with his wife – novelist Blythe Woolston – and their two children.