Once seen only among an older population, adult diseases such as fatty liver disease, hypertension and osteoporosis are being diagnosed more and more in children. And you can add to that sleep apnea, Type 2 diabetes and high cholesterol levels. The culprits? Unhealthy diets and growing waistlines, experts say.

Recognizing obesity early and appreciating the cardiovascular decline it can pose for young children has become so important that the American Academy of Pediatrics established guidelines and recommendations for pediatricians, typically not accustomed to seeing the resulting cascade of health issues in their patients.

“Several studies have shown that obesity is underrecognized by parents as well as by physicians,” said Dr. Seema Kumar, pediatric endocrinologist at the Mayo Clinic Children’s Center. “Parents in general tend to think they will outgrow it. … It also depends on the ethnic group they’re coming from. In some cultures, being overweight is actually a sign of prosperity. So they may actually not even consider that as a problem.”

Kumar’s observations ring true with a study by the New York University Langone Medical Center that was published online in the journal Childhood Obesity. While rates of childhood obesity have risen over the past several decades, the study showed, a vast majority of parents perceive their kids as “about the right weight.”

The researchers also compared these 2012 survey results with those from a similar survey in 1994. Not only were the children in the recent survey significantly heavier, but the likelihood that parents could identify their child’s weight accurately had declined about 30 percent. Dr. David Katz, the director of Yale’s Prevention Research Center, has coined a word for the problem: “oblivobesity.”

“Parents cannot ignore the threat of obesity to our children and still hope to fix it,” he wrote in an editorial accompanying the new study.

One reason parents may have difficulty perceiving their child’s weight is because of the “new normal”: Children are generally becoming heavier. But Katz also cited parents for “willful, genuine denial.”

Dr. James J. Maciejko, a lipidologist and director of the Adult and Pediatric Lipid Clinics at St. John Hospital in Detroit, is concerned by how few Americans in general understand the grave dangers of overeating. Maciejko sees kids eating 3,000 calories a day and reminds them and their parents that young bodies cannot handle that load. In general, he said, prepubescent children should be consuming about 2,000 calories per day; if they are quite active, maybe 200 to 300 calories more. After puberty, most boys should consume about 2,000 calories a day and girls about 1,500 to 1,600 daily. Why? Here’s the list:

Heart disease

With obesity comes the risk of cardiovascular disease. Developing risk factors in childhood can greatly increase the likelihood of heart disease in adulthood. For that reason, guidelines sponsored by the National Heart, Lung and Blood Institute recommend that all children be screened for high cholesterol at least once at ages 9 to 11 and again at 17 to 21.

Diabetes

Overweight children can develop “adult-onset” diabetes, or Type 2, as young as age 8, and the Centers for Disease Control and Prevention points out that the loss of insulin sensitivity can develop at any age, especially among overweight children. The complications from diabetes are many: cardiovascular problems, damage to the nerves, kidneys, eyes and feet, and it can contribute to Alzheimer’s disease.

Hypertension

“There are enough studies that have shown that … an overweight child is two to three times more likely to have high blood pressure compared to a child that is normal weight,” Kumar said. Hypertension can cause a range of health problems, from the heart to the brain to the kidneys.

Fatty liver:

Maciejko said he is noticing more children being diagnosed with hyperlipidemia, or high fat levels in the blood. Part of the reason simply may be that doctors now are testing children for this. The pediatrics association “now recommends all kids by the age of 9 have a lipid profile,” he noted. Fatty liver disease can lead to depleted liver function, and the consequence of high triglycerides is cardiovascular disease, among other things.

Osteoporosis

Just as important as what kids are putting into their bodies is what they’re not. Eating disorders among very young children are contributing to the increase of osteoporosis, said Dr. Ellen Rome, head of the Cleveland Clinic Children’s Center for Adolescent Medicine and professor of pediatrics at the Cleveland Clinic Lerner College of Medicine at Case.

“So many of the problems we see in adulthood have their roots in childhood,” Rome said. “A classic example is osteoporosis. That’s now seen as a pediatric disease.”

“If a kid from childhood isn’t getting three calcium or dairy servings a day with vitamin D, they can, in their early years, not be putting on the bone they’re supposed to have put on,” Rome said. By not depositing bone during those early years in life, when they’re supposed to be adding 40 to 60 percent of their bone mass, they’re increasing their risk of osteoporosis later in life.

So those health issues all link to the diet problem. What can parents do? Helping children develop healthy eating habits now is the key, the experts say, because the dire consequences are coming fast.

The New York Times contributed to this report.