After one of his first days of school this year, my 7-year-old son, Joey, in between details of his trip to the library and descriptions of his new second-grade classroom, casually imparted the following tidbit about his day: He had eaten "most" of the lunch I carefully had packed for him, then dipped into his milk-money account for a bag of tortilla chips at the cafeteria. To my shocked look, he said, "What? It was only 167 calories."

Geez, I thought, he actually looked. But my moment of self-congratulation ended quickly. He obviously had set aside the perfect, juicy peach I had given him and eaten a bag of salty, fatty, fake-flavored chips instead.

Joey's 12-year-old sister, Matilda, did eat her healthy lunch — partly because it had been planned and negotiated with the same care as her first-day-of-school outfit. A tuna sandwich on wheat? Too smelly — "It makes a bad first impression when you open up something that smells weird," she told me.

So into her designer lunchbox went the flavored water favored by her posse of friends, a lean ham-and-cheese with reduced-fat mayo on wheat bread, a yogurt and a nice peach.

With kids' school firmly in session, the air waves — and my e-mail in-box — are full of clever ideas on lunchbox nutrition.

The experts' tone is upbeat and cheery, but there's a subtext of fear and dread: The rise in child obesity will steal your children and rob them of their happy futures. So, Mom and Dad, you had better rethink those slovenly lunchbox choices and your reliance upon nutritionally suspect school lunches, and get with the program.

As my kids illustrate, it's not always easy. If they're going to eat it — and not the many junky alternatives available to them — they have to be on board with a lunchbox's contents.

The experts don't tell you how to find the levers that will encourage them to choose healthy foods. Like so much in parenting, that's one of those things you have to learn on the job.

These experts should come to the grocery store with my two kids and me for a lesson in what they are up against. And they might see a ray of hope too.

I took the kids to our well-stocked neighborhood grocery store (not, by the way, a resource that all kids have) and gave each one a basket.

First, I asked each to put into the basket the things he or she would like most to put in a lunchbox. Then I had each kid troll the aisles and choose healthy lunchbox items that he or she would be willing to eat (say, rather than set aside in favor of chips) every day.

JUNK-FOOD IMPULSES

The worst fears of U.S. nutrition experts would be confirmed by my voracious son. Joey's nutritional impulses demonstrate clearly what will happen if American children are given free rein to graze, "Lord of the Flies"-style, on an American landscape rich in salty, sugary, fatty temptations.

He is an indiscriminate eating machine programmed to prefer the highest-calorie victuals he can find, and he'll snarf down anything that's not nailed down. He also still takes those TV ads aimed at kids at their word, so if they say that some gummy fructose-laden roll-up is part of an active (read: "healthy") lifestyle, he'll be all over it.

Joey tackled his first challenge with gusto, and it wasn't long before his basket was overflowing with peanut-butter candies; packages of potato chips with text messages imprinted on them and some kind of dipping sauce; cookies in all shapes and sizes; those packages of bright-orange peanut-butter and cheese crackers (his version of a sandwich, I guess); bologna; and a six-pack of neon-colored "sports" drinks. He sidled up to the doughnut case and, one by one, pointed to its contents as desirable lunchbox options.

"I would never buy all this stuff," he says — a claim I seriously doubt. "It's got way too much sugar. I'd weigh 1,000 pounds," he adds. OK, I think, so I have taught him something. Still, he's positively giddy with the pleasure of picking it all out.

On the second — healthy — round, Joey did just a little better. The bright-orange crackers were still there. The double-chocolate cookies gave way to fig bars, fruit-flavored cereal bars and the reduced-fat versions of some salty snack crackers. But a bunch of bananas had made their way into his basket, and some of those little tubs of cut-up fruit in light syrup. The bologna stayed, but it was turkey bologna.

With his rudimentary reading skills, Joey recognizes the "reduced fat" label on food packaging and assumes it to mean healthy. If it contains fruit — or fruit flavoring or even fruit in the name — it must be good. And — I'm ashamed to admit it — if I have bought it for him before, he assumes it's probably healthy. Of course, none of these is necessarily true.

ARE LABELS TRUTHFUL?

Matilda should give the child-obesity experts hope. Her first — anything you want — pass and her second, healthy, trip down the supermarket aisles yielded many of the same choices. Both times, she chose strawberries, fat-free yogurt and vegetable-rich soups labeled as "lower in sodium" and "a good source of fiber."

Cans of low-sodium vegetable juice were in both the before and after baskets "because my friend Molly says it's delicious," said Matilda, pointing out the "Heart Healthy!" label. She thought she would like to try pomegranate juice, rich in antioxidants, because her best friend forever Alex loves it (and it's in that adorable bottle).

She picked out sunflower seeds because her friend Asia's dad likes them. Though they have a fair amount of fat, they're a good source of protein, she said, turning the jar over to read the label. "And these are unsalted," she noted earnestly.

Like most adults, Matilda tended to be drawn in by the manufacturers' promotional nutritional seals, such as "best life" and "heart healthy," which sometimes don't tell the whole nutritional story.

But she frequently checked labels and seemed to look for evidence of real ingredients, such as vegetables. That said, she didn't spend much time in the produce section itself.

'A TEAM EFFORT'

Helping kids to recognize — and want to eat — healthy food "is a team effort," says Pamela Ofstein, the director of nutrition for e-diets.com.

Parents should view packing lunch as a teaching opportunity about which foods are healthy, why and what portions are appropriate, and they should give kids choices and let them help, she adds. That, says Ofstein, is the best way to turn a nutritional wild child into an adolescent with good instincts about food.

And, she says, letting kids play a role in filling their lunchbox make it more likely they'll eat the good stuff once they're at school.

So, it's back to the shelves with the cheese crackers, chips and cookies. Bring home the bananas, the low-sugar cereal bars and take two of everything Matilda picked.

Oh, and memo to self: Write the cafeteria lady and tell her the milk-money account is only to be spent on milk!