When American kids reflect upon their childhoods decades from now, snacks may figure more prominently in their memories—and around their waists—than meals shared around a table.

From 1977 to 2006, American children have added 168 snack calories per day to their diets, a study finds. They're munching cookies after school, granola bars on the way to piano lessons, chips after an hour of soccer practice and peanut butter and crackers while waiting for dinner. For some, those extra 1,176 calories a week could amount to as much as 13 1/2 pounds of body fat a year.

Those non-meal noshes now account for more than a quarter of their average daily caloric intake, said Barry M. Popkin of the University of North Carolina at Chapel Hill, author of the study published in the journal Health Affairs.

The research establishes just how much the omnipresence of snacks - and the $68-billion-a-year industry that sells them - has contributed significantly to an epidemic of excess weight among U.S. children.

But even as public health officials remove sodas and fat- and salt-laden snacks from school vending machines, parents hoping to roll back the tide of snacking face some daunting challenges, including a food industry dedicated to satisfying the nation's voracious between-meal appetite with snack wraps, burger bites and miniature candy bars marketed as midafternoon pick-me-ups.

Charlene Miller, a South Pasadena mother of two boys, said, "There's a lot of peer pressure" to ply kids with treats. At the beginning of basketball season this year, the coach of her 6-year-old son's team ignited a parental rebellion when he said there was no need for an organized snack after the kids' Saturday morning games.

"Some parents got really upset and said, 'But our kids expect a snack,' " Miller said. The coach relented, and each of Charlie Miller's teammates regularly gets a "snack bag" - often chips, a packet of fruit-flavored candy and a sports drink -- before going home to lunch.

Dr. Judy Palfrey, president of the American Academy of Pediatrics, said the study's findings pointed to one of many factors that had pushed the nation's rate of child obesity to 16.4% in 2007 - an increase of roughly 10% since 2003 alone.

"We see milk intake and meal intake are going down; the consumption of fatty and salty foods is going up. Everybody is very busy, on the go all the time, not having three meals at home," Palfrey said. American families need to "think about healthier replacements" for between-meals food, she says, and they need to hear those messages from their children's physicians.

"Remember the days when we used to get quartered oranges? Bring those back!" Palfrey added.

In 1977, just under 75% of kids between 2 and 18 consumed at least one snack between meals, according to the new study, which tallied the responses of 31,337 children and adolescents to four federally funded food surveys. In 2006, the proportion of kids who snack reached 98%.

That surge in snacking has pushed kids' overall intake of daily calories to an average of 2,099 a day - up by 100 calories a day since 1977, the survey reports. By 2006, 27.3% of the total calories - just under 600 calories a day - came in the form of snacks, the North Carolina research team found.

Meanwhile, calories consumed at mealtimes have begun to slide slightly since the last food survey was conducted in 1994. The result: U.S. children are consuming more fatty, sugary and salty foods and less of the dairy, protein and produce that predominate at mealtime.

Sweet snacks such as cookies, cereal bars and cakes continue to supply the largest share of snacking calories, but the number of calories consumed in salty snacks such as popcorn, crackers and chips more than doubled from 1977 to 2006, the study found.

Study coauthor Carmen Piernas, a researcher at the University of North Carolina at Chapel Hill, said very active kids could burn snack calories through growth and physical activity, but children who are inactive, whose growth has slowed or whose diet is otherwise high in fat, will pack more of those calories not as muscle but as fat.

The snacking habit starts early, she added: Children 2 to 6 had the highest rate of snacking of all the groups surveyed.

Overall, snacks have become an integral part of American children's mobile and highly programmed lives: Toddlers en route to play groups are plied with nibbles in the car to stave off tantrums; school-age children are met with energy bars for the ride to lessons or sports activities; older kids graze as they contemplate homework and check their Facebook pages.

"They come home from school, they have a snack; we go somewhere in the car, we have a snack. We might get caught somewhere, and we should have some snacks just in case," says Katie Scrivner, a Los Angeles mother of three. "It's never-ending snacks around here."