Q: I am the 36-year-old mother of a 4-year-old. I am quite happy with our family size, but recently I have received many well-meaning comments to the effect that our son "deserves" a sibling.

I want to return to work soon; I enjoyed it so much and have found motherhood to be a very isolating experience. Please share your feelings on "onlies." The dilemma has been on my mind a lot lately.

A: Parents have been getting advice ever since they've been begetting, but that doesn't mean you have to listen. The size of your family is your own business. Many couples want more than one child, which is fine for them, but you're molding a family to suit your own style.

You and your husband are the only ones who can make such an intimate, critical decision, and if you pay attention to your hearts, it will be the right one.

If you need to feel better about your decision, remember that your little boy is probably quite content with the way things are. While an only child may beg for a little brother or sister (or kitten), he won't want to share his "only" parents and all the attention he gets.

The well-meaning comments you're getting now can't be anything new. When you were childless, there must have been those who told you that life without children was no life at all, and now that you have one child, they urge you to go for two. And if you have two children, you can bet that some people--and possibly the same people--will say how sad it is that they are the same sex (or that they aren't), or ask if you know that life is passing you by. And if you have three children (or heaven help us, four or more), you will get lectures about the population explosion or remarks about "surprises," as if you hadn't wanted your babies.

Most of these remarks are merely verbal minuets, a way of talking without really saying anything.

Close friends and family, however, tell you what to do because they care about you. They like the job you've done so far and they want you to have what they have in life--or wish they had. This doesn't mean they're right, or that it's easy to hear, particularly since you feel isolated.

Everything can seem so trivial now. Your time is chopped into 20-minute chunks--some good, some bad--and there is no such thing as a perfect day. This makes self-doubts inevitable, especially when the well-intentioned give you their good advice. Somehow they forget how hard it is to be a full-time mother, how lonesome you can feel and how much nerve it takes to reach out for friendships when you can't handle your young friend at home.

Loneliness is really the crux of your problem. Unless you can build a network of candid, caring friends who are going through the same experience that you are, another child would only make your isolation worse.

As always, it's best to follow your instincts. If you think a job is best for you, that's that: It is best. Work should give you the confidence and friendships you've been missing, although you shouldn't expect it to be as easy as before.

You'll probably feel fragmented for years, as you try to juggle your house, your job, your child and all the bake sales, meetings and car pools that parenthood entails. This is supposed to be easy for some women, but most feel swamped, until they realize they can't be Supermom--and no one else can either.

When you reach that blessed state you'll discover something new about yourself: Your child has taught you much wisdom and patience, and given you such an ability to love, that you and your husband may find that the idea of another baby is irresistible.

This would be great because you would be planning another child to please yourselves, not your friends and neighbors, and certainly not your 4-year-old. A baby is not a toy.

Your child doesn't "deserve" a new baby, but he does deserve a joyful home and he'll get it if his parents are happy and their marriage is strong. It's stability, not siblings, that makes a child thrive.