Q. "My 13-year-old wants to start baby-sitting for a family with two small children, but I'm not sure she's too young or what her duties would be. We live in Georgetown and they are nearby."

A. While 13 is too young for some children to sit, most of them can handle early jobs on Friday or Saturday nights. We say "early" because there is always the prospect of a fire, a burglary or a convulsion. A sitter shouldn't go to sleep unless she can awake at the first strange sound, which may not happen for one to two more years.

To be a good sitter your daughter needs self-confidence, and experience is the only way to get it. Unless she already is handy with diapers and bottles, she should give a few free afternoons to help the young family (a small investment to learn skills for which she will be paid well in the next few years).

Your daughter may find it easier to handle the children than the parents.

They may give excellent instructions about their children (most parents do), but hardly mention the pay and the perks: food, TV, company and the telephone. A child's interpretation of her privileges -- or the parents' idea of their rights -- can cause bad misunderstandings unless they are talked about first or at least afterward, so they don't happen again.

Because many parents treat sitters on a social basis, they have trouble being straightforward with them. If so, your daughter will have to be the one who is direct, both before she accepts the job and again when she goes to the house. If the parent doesn't say when she calls, "I pay an hour; is that all right?" the child is obligated to say, 'I charge an hour; is that all right?"

There also will be those parents who will try to chisel a sitter out of a half-hour, which few teen-agers can handle. You can help her realize that she knows them better than she did before, and that she need never sit there again.

When your child sits for a new family, she should be hired to get there 15 minutes early (at their expense), to meet the children and get those excellent instructions: bedtime rituals; location of the diapers and the diaper pail; special books and magic blankets; foods the child can eat and when; medicine to be given (in writing); numbers of the peditrician and two neighbors, in case of emergency -- hopefully pasted on each extension phone, along with 911, -- and, of course, the telephone number where the parents can be reached.

The sitter needs instructions about the house, too. People are so used to peculiarities around them that your daughter may have to ask if there are special locks or alarm systems, and if there are dogs or cats or tenants that might go bump in the night.

She also may have to ask what she may eat for a snack or supper, for she shouldn't go hungry. But she shouldn't help herself to everything either. A good sitter finds out if the children may watch TvY, and which shows, and if she may use the telephone after they are asleep. Generally she should leave the phone free 50 percent of the time, so the parents and other callers can get through.

Even if the parents tell your daughter she can invite a friend to keep her company it's a bad idea. Baby-sitting is a job , and you don't bring company to work. If your daughter says she is afraid to sit alone, then she's too young to sit. If she says it's too boring to sit alone, she needs a more interesting job. And if, in a year or two, she asks to have a date while she sits, suggest cold showers instead.

Some parents expect both baby-sitting and housework. The person who considers her child so terrific that his company is payment enough may ask your daughter to vacuum and do last night's dinner dishes, which is nonsense.

Of couse a sitter should put the living room in order after she and the children play leap frog over the sofa cushions, and she should wash any pots and plates they use. But she doesn't do day work unless she gets the minimum wage. Your child either will have to say so, or simply not do the work.

If baby-sitting does nothing else for a child it teaches her -- and perhaps the parents -- that for every quid there's a quo .

Even though your child is old enough to sit for others, she is still your child. The first time someone calls her to sit, you need to talk with this person too. You don't interfere with the money arrangements, but you do ask what time the parents expect to be home; request that the house be well-locked when they leave and make sure they will pick her up and take her home if it's dark, even if it's only a block away.

For the parents who drink too much and expect to drive her home anyway, your child should be schooled in a discreet set of signals. A teen-ager usually would drive with a drunken orangutan before she would complain, but she can say, "My dad is coming to pick me up." Nothing else need be said. Don't worry that she won't let you chew them out. To lose a good sitter is punishment enough.