Other parents, when they think of their child's first day of school, may remember the catch in their throat as they watched their child pass through the classroom door.

Whenever I recall the day six years ago when my oldest entered kindergarten, I think of lunch boxes.

Kindergarten was supposed to last all day, so my son, like the others, brought his lunch. We parents did not know that the kindergarten program had been cut back to half a day for the first two weeks in order to ease the children into the school routine.

Many of us were disappointed, but one mother's disappointment went beyond the rest.

"My child," she announced in a voice loaded with emotion, "has been looking forward to eating out of a lunch box for two years. She's come with her lunch box -- and she's going to eat out of it."

She did -- on the school playground, with her mother lookin on.

Lunch boxes, obviously, are big deals.

To a small child, they are a ticket into the big time.

To an older one, they are an emblem of the image he or she wants to project.

To all children, they are a harbinger of fall. An expedition to select a new lunch box is a pleasant way to focus a child's thoughts on school.

Lunch boxes are not all alike. They are made of different materials, come in shapes and sizes that differ significantly, enclose different styles of thermos bottles, and present varying images to the world.

"Lunch boxes either rust out or break," says one mother who ought to know. She has six children. "The metal ones rust and plastic ones break." Plastic boxes are easier to clean and stay "new" longer, but are far less sturdy.

Cardboard-covered vinyl is a third material that lunch boxes can be made of. Ones made of this should be avoided at all costs. The manufacturer says not to submerge them in water, but after several weeks of crusty peanut butter and tuna fish build-up in the seams, a little voice inside you will cry: Do it, do it. After you've done it several times, enough water will seep through the seams to affect the rigidity of the cardboard. Good-bye lunch box.

Lunch boxes come in three geometric shapes: trapezoid, rectangle, and cylinder.

Trapezodial lunch boxes are the old-fashioned kind with the thermos carried in the top. They are the roomiest. A thremos, an insulated snack jar, a sandwich, and even a cookie or a piece of fruit will all fit inside.

Rectangular-shaped carry the thermos alongside the food, and can usually accommodate an insulated jar and a sandwich or a piece of fruit, but generally not all three.

Lunch boxes shaped like cylinders, with a carrying strap over the top, are invariably made out of vinyl-covered cardboard, so they are double losers. Their shape is such that even a sandwich tends to get smushed. They must be for girls who want to lose weight.

One mother describes a thermos bottle as a deep, dark place especially suited to the growth of organisms. Thermos bottles are the bane of all banes -- persistent pests that sit on the kitchen counter day after day demanding to be washed. The person who invents a thermos bottle that is dishwasher-safe will become rich.

Wide-mouth bottles are better than bottles with narrow mouths because they are easier to clean and can carry soups and stews in additon to beverages. They are made by Aladdin. Narrow-mouth bottles are made by the Thermos division of the King-Seely Thermos Co.

Last year the Thermos people came out with an engineering marvel that is a mother's nightmare -- a Flip 'n' Sip cap. The cap has a little spout that flips up so that a child can drink out of it directly or insert a straw into a little hole. The cap is made out of three interlocking pieces that come apart for cleaning. Each piece has nooks and crannies to harbor microorganisms. This year Aladdin has come out with a two-piece Pop-Top. Neither cap provides as much insulation as the old-fashioned type.

Lunch boxes come in and go out of style. I don't have to cast my memory back to may years to remember the time when Batman was all the rage.

Most kids want a new lunch box every year. One mother reports on six serviceable lunch boxes line up in her basement like so many tombstones in a graveyard of past fancies.

Many of the lunch boxes headed for fall popularity represent recent movies or popular TV shows: "Superman II," "The Fox and the Hound," "The Legend of the Lone Ranger," and the "Dukes of Hazard."

For kids in the primary grades, there are lunch boxes depicting Scooby Doo, characters from "Sesame Street," the Flintstones, Strawberry Shortcake, and a collage of super-heroes. For older kids there are lunch boxes featuring characters from "Peanuts," the Muppets, and Walt Disney. Especially for boys are scenes from outerspace and sports-oriented designs. By the time a child leaves elementary school, he usually trades in his lunch box for a paper bag.

The greatest variety of lunch boxes can be found where the kids are -- in the suburbs. In the city, People's and Murphy's have good supplies. Prices at stores I visited ranged from a low of $3.78 at Toys 'R' Us for a lunch box with thermos to a high of $6.48 at a D.C. Murphy's. (The same lunchbox was 19 cents cheaper at Murhpy's in the suburbs.) Most cost between $5 and $6. Memco and Woolco have good supplies of unbreakable thermos bottles sold seperately.

"When my child started kindergarten, it was a half-day program," reports one mother. "Midway through the school year, it was expanded to all day and I went out to buy a lunch box. They were all gone."

All she could find was the traditional black workingman's lunchbox, unappealing in itself and including a glass thermos.

Lunch boxes are like biscuits: You got to get 'em while they're hot.