Atmosphere: A fiesta of Mexican fare, with different menus for the pleasant outdoor cafe and the cozy restaurant inside.

Price range: From good-sized meat or chicken tostadas at $1.75 to an indoor selection of many dinners under $5.

Hours: Mondays through Fridays indoors from 11:30 a.m. to 3 p.m. and 5 p.m. to 11 p.m., outside from 11:30 a.m. to 11 p.m.; Saturdays, in and out, from 5 p.m. to 11 p.m.; closed Sundays.

Special facilities: Accessible by wheelchair. Seating for small children can be arranged. Street parking usually possible.

Reservations: Not necessary.

Credit cards: American Express, Master Charge, Visa.

This is mostly a tale of two ravenous urchins, an evening outdoors and a do-it-yourself taco kit. And if you stick with us long enough, we'll wind things up with a side-trip for dessert.

The cast of characters, in order of appearance at my office on this Friday evening, begins with our 11-year-old son, eagerly followed by a congenial contemporary who is astounded to discover that one of the top editors at The Washington Post has a Nerf-ball basket-net stuck to her office window.

As they were sneaking free throws, my wife arrived, doing her best to pretend she had nothing to do with this invasion.

To our relief, the boys had a sudden attack of good behavior and a gnawing in the craws, which - once I mentioned the operative word "dinner" - ended their game without overtime.

We headed for La Fonda, a restaurant known to many older hands hereabouts as a fine, intimate Mexican dining room. But now it's more than that, for there's a jolly little sidewalk cafe with its own special menu of delights.

There arose the immediate question: Would the cafe fare be sufficient to fuel our young hungries without too much afterburn, or should we move inside for the meal?

It was far too pleasant at our little white table next to the geranium bed, below the gargoyles, the balconies, the weathered wooden shutters and the wrought-iron grillework for us to turn inward. Besides, how else could we watch the kid who was rolling around the street on a perilously tall unicycle, or the strollers from all walks of life?

Still, while sipping Cokes and margaritas and munching from a basket of tostadas with hot sauce, we did compare the indoor and outdoor menus for an idea of variety and prices.

Inside, where the dimly lit, cozy rooms are walled with Mexican tiles, oil paintings and hand-made ceramic plates, the appetizers and salads go for below $2 and there's anything from chili con carne at $3.75 to steak at $7.95, with many a rendition of chicken in the $4.75-$4.95 range.

But back near the red-white-and-green Medaglia d'Oro Espresso umbrella, our foursome found plenty of modestly priced dishes to test outdoors. First up was my experiment in soup, entitled Sopa de Lima, "a hearty Yucatan soup with chicken," at $1.25.

It was hearty enough, with what seemed to be reeds of shredded taco, a slice of lime and three thin slices of hard-boiled egg in a clear and salty broth. Though each of my three taste-takers pronounced it much too salty, I forgot to be bothered by that.

With a little help from our friend the waiter, the boys hit the jackpot by sharing "Antojitos de Montezuma," which is La Fonda's make-your-own-tostada-and-taco kit, for $4.75.

The makings, which arrived neatly arranged on a tray, included shredded beef and chicken, cheese, tomatoes, hot peppers, sour cream, refried beans, lettuce and slices of avocado. Consider the possibilities for combinations here, multiply by two and you get an idea of what the boys were able to pack away.

That much taken care of, they went on to request an order of Taquitos de Carne - three tacos rolled and stuffed with meat, sour cream and various other trimmings, for $2.50. That's what I had, too, without the sour cream.

Another ole for my wife's selection: tortilla with guacamole and sour cream (you could easily hold the sour cream on this one, too), for $1.95.

Between the outdoor cafe and the restaurant, you should be able to find just about anything your Mexican appetite might desire, from gazpacho with beef tostado to bean soup with chicken taco to spicy meat pastries to salad with shrimp and avocado - each under $4.50. Our own bill for everything came to $19.20 plus tip.

But don't leave yet, for the boys had a grand design for a test of gastronomic fortitude: We motored over to 1531 Wisconsin Ave. NW, better known as The Parlor, in Georgetown (337-9796) - where ice cream is king under the trees and lanterns on the brick patio out back.

My wife's hot fudge sundae ($1.40), with coffee (50 cents), was certainly a civilized enough finale. But it was all we could do just to watch our son emptying a mugful of hot fudge, scoops of ice creams, whipped cream, marshmallow and probably anything else that contains a least 4,000 calories a spoonful, for $1.85.

Throwing moderation to the winds (or the gentle evening breeze, as it were), our son's effervescent partner-in-fudge polished off a (shudder!) banana spilt, at $2.25. I played goodie-two-shoes, making oh-so-much of the fact I was just sticking to coffee. This all came to $7.02 plus tip and a couple of laps down the avenue to walk some of it off.

Note, please, that the two-stop tour is neither mandatory nor necessarily good for you.There is happiness enough at La Fonda without stepping into The Parlor. But the Parlor-parlay is the perfect punishment for gluttons.