Atmosphere: Warm and informal.

Price Range: Moderate. Lunchtime entrees range from $2.75 for quiches to $4.00 for some of the daily specials. Prices are 25 per cent higher in the evening.

Credit Cards: Master Charge, Bank Americard/Visa.

Hours: Monday through Saturday. Lunch 11:30 a.m.-2:00 p.m.; dinner 6:00-10:00 p.m. Closed Sundays.

Special Facilities: None, really. No high chairs or boosters are provided. But the restaurant is at ground level and should be accessible to the handicapped.

Reservations: Accepted for luncheon parties.

What do you do when you are walking home from the library with your children, it's lunchtime, their feet hurt and there's not a burger haven in sight? Well, you simply steer them into an appetizing-looking restaurant, announce that everyone is on his P's & Q's, and you have lunch out. It's really not so outlandish.

Recently, on just such an occasion, a friend and I with our little ones in two tried L'Estaminet, a small French cafe in Old Town Alexandria, and found it a real treat not only for the children but for us as well. The children left feeling they had done something very special, and we adults had had a civilized lunch.

In French, L'Estaminet means a small bistro or cabaret, a perfect name for this cozy little eastery with its red-checked table cloths, beamed ceiling, and stuccoed walls covered with posters and scenes of Paris.

A black slate propped up outside the front door announces the day's specials. And if that little scene doesn't make you nostalgic for Paris, the chalked up menu will. The specials change daily. The day we tried L'Estaminet, the slate offered perch in white wine sauce for $3.95; poulet basqueaise, $3.95; mussels poulette, $3.50, and scallops, $4.

We arrived shortly after noon, and by 12:30 almost all the restaurant's 14 tables were filled.

If L'Estaminet has a deficiency, it is the service. One harried waiter was trying to serve everyone, and we waited about 20 minutes before our order was taken. Then we waited a while longer for the food. But when it emerged from the kitchen, our meal was a delicious reward for patience.

My friend chose the perch, done in a white wine sauce flavored with tomato. The sauce was delicate and delicious and really enhanced the fish.

One of the children asked for Quiche Lorraine, $2.75, on the regular menu. It was all gone, so quiche sans Jacques (with spinach) at the same price came as a substitute. The other child wanted a ham sandwich, so we ordered the French variety - the croque monsieur, $2.50, which is a ham and chesse sandwich made with French toast and sauced with a cream sauce. It was a great success. The toast was cruncy, crisp and cheesy, the sauce not at all heavy.

But my mussels, done with a very light cream sauce, were the hit of the meal. They in a bowl, black shells gaping, with about 18 tender little mussels swimming in a delicious winey brew, which I ate with a spoon when all the shells were empty. I also had to fend off my 3-year-old, who after he had tasted one mussel wanted the whole plateful.

The quiches came with a small green salad dressed with a light vinaigrette. The perch was accompanied by small roast potatoes. The mussels came all alone, but you can order pain buerre, or bread and butter, for 45 cents. I dearly wanted something to mop up the mussel sauce, but the waiter was so busy I skipped it.

L'Estaminet has onion soup for $1.50, and vichysoisse for $1. And there is a very good crab quiche for $3.25. A modest wine list is available as well.

Our bill for the meal, which had included two Cokes for the children and hot tea for the adults, came to a fairly reasonable $15.45, excluding tip.

L'Estaminet is open in the evenings as well, and prices are from 50 cents to $1 per item more expensive. Portions are slightly larger, however.