Caffeine-infused waffles and maple syrup are being promoted as energizing alternatives to a morning mug of coffee.

But the recent craze of adding caffeine to a range of kid-friendly snack foods — including popcorn, chewing gum, candy bars, mints, Cracker Jack, jelly beans and ice cream — is raising enough concern that the U.S. Food and Drug Administration (FDA) has launched an investigation of caffeine's possible health effects on children and adolescents.

The effort, which comes amid the heated debate over whether energy drinks with stimulants are safe for children, marks the agency's first close look at the world's most popular psychoactive drug since its use in cola was approved in the 1950s.

Most healthy adults can safely tolerate moderate doses of 200 to 300 milligrams, which is about two to four cups of brewed coffee, the National Institutes of Health said. But the United States lacks official guidelines or limits for children, whose smaller bodies and developing brains may be more vulnerable to caffeine's effects, including the risk of physical dependence and addiction.

Part of what worries the FDA is the changing nature of how caffeine is delivered — through a greater array of products that may appeal to younger consumers and in higher doses than in the past.

Chewing a pack of Jolt Energy Gum, for example, would have effects similar to downing six energy drinks, according to the package.

"It's a question of finding caffeine in new and different places," said Michael Taylor, the FDA's deputy commissioner for food. "There are concerns over the perhaps subtle developmental impacts on kids and whether they become regular users of a central nervous system stimulant. What are the cumulative effects?"

Meanwhile, parents can't necessarily tell how much caffeine kids are getting. Caffeine levels aren't required to be disclosed on food labels, and if the caffeine occurs naturally — as in tea or cocoa — it isn't listed among the ingredients. In the case of energy drinks, many are sold as dietary supplements and don't have to disclose caffeine levels if the ingredient is part of a "proprietary blend."

Proponents say caffeine has been safely consumed in foods and beverages for centuries. Many of the newly caffeinated snacks target adults who want a quick pick-me-up but don't like coffee.

It's in the brain

Consumed daily by 80 percent of the world, caffeine is a bitter-tasting nervous system stimulant that occurs naturally in coffee, tea, guarana and kola nuts. It's thought to work by interfering with a brain chemical called adenosine that facilitates sleep.

"It not only wakes up the brain, but it can increase heart rate," said Dr. Lynn Goldman, a pediatrician and dean of the School of Public Health and Health Services at George Washington University. "When I've seen people with caffeine overdose, they're scared; they end up in the ER because they think they're having a heart attack."

In adults, caffeine use is relatively safe. But the American Academy of Pediatrics recommended in 2011 that children and teens steer clear of caffeinated drinks because caffeine interferes with sleep and can contribute to anxiety, in addition to an increased heart rate.

"Childhood and adolescence is a period of rapid growth in the final stage of brain development; proper sleep and nutrition are essential," said Jennifer Temple, an assistant professor in the School of Public Health and Health Professions at the University of Buffalo who studies children's caffeine use. "Caffeine disrupts sleep patterns, and the excess consumption of soda is associated with poor diet, excess weight and cavities."

The most recent federal data show that children ages 2 to 13 ingested an average of 43.5 milligrams of caffeine a day in 2008. A typical cola contains about 35 milligrams in a 12-ounce can. Young men ages 14 to 21 consumed 110.5 milligrams per day; women took in slightly less. Current regulations include the FDA limiting the caffeine content in soft drinks to 71 milligrams per 12 fluid ounces. But manufacturers often circumvent the limit by calling their products dietary supplements; some energy drinks contain as much caffeine as five cups of coffee.

Sales of energy drinks grew by 78 percent from 2006 to 2011, according to the market research firm Mintel, and a recent study in the journal Pediatrics found that half of the energy drink market consists of children, adolescents and young adults.

Energy drink consumption has been associated with elevated blood pressure, altered heart rates and severe cardiac events in children and young adults, especially those with underlying cardiac disease, according to a letter sent to the FDA by more than a dozen prominent researchers and scientists. Dr. Steven Lipshultz, a pediatric cardiologist at the University of Miami, tells parents that young patients with an underlying heart condition should avoid caffeine because it can stimulate the heart.