I'm going to have a baby in six months and my husband and I are very excited about it. This is my first child and he has three children from a previous marriage -- two girls, 16 and 13, and one boy, who is 8.

My husband plays an active parental role and has a joint custody arrangement. We see the children two nights during the week and every other weekend.

I've adjusted well to stepparenting and we all get along fine.

Money is the only problem. My husband pays $1,000 a month for child support, but the children -- especially the girls -- complain. They say it isn't enough money for camp and for the clothes they want and sometimes they say he is cheap.

We explain that we do all we can -- we honestly do -- and that there isn't enough money to go around.

How will the baby affect our family, his ex-wife and children? Will they be jealous? What can we do to prepare our family for this new child? What can I expect?

Since change is always threatening, you can expect the new baby to make the children -- and the ex-wife -- a little jealous. If you keep treating the children fairly and honestly, however, they soon will feel secure.

Nevertheless, the children still will want more than they can have, baby or not. That's just human nature and it shouldn't cause you a single twinge of guilt. Children aren't supposed to be spoiled.

Their child support (and it's not shabby) sounds like enough to pay for their shoes, their coats and their basic clothing, but teen-agers always want more than that. And they should pay for it.

Although your stepdaughters don't get paid for doing chores and baby-sitting at their two homes -- a family is not a business -- the 16-year-old can work in a shop on weekends and the 13-year-old can baby-sit for other families on Friday or Saturday nights.

With this money they can buy some inexpensive, trendy clothes and pay the difference in cost between basic and designer jeans. With your guidance they can fill out the rest of their wardrobe with a few good sweaters and accessories at a classy thrift shop. It's time they learned that second-hand clothes are better than new ones, if the quality is better.

They'll learn other lessons too -- like how hard it is to amass money and how carefully it should be spent. Above all, they'll feel like part of the home team. This is important in any family, and particularly a stepfamily. Although grown-ups run the show, children want to be responsible players.

It may not be apparent, but teen-agers have a terrible need to learn how to survive in an adult world, just like a 2-year-old practices his climbing and running and jumping and an 8-year-old feels required to listen to his mom on the phone. In every case, they're trying to master the skills they'll need to get along when they're a little older.

There are other ways to teach your stepdaughters to live within their income and yours.

They'll accept the situation better if they see how the family money is spent, as long as it doesn't make them feel like a financial burden.

A 16-year-old -- even a 13-year-old -- can work with you to sort checks, note those that are cleared, add any deposits that aren't listed on the statement, deduct the outstanding checks and help you draw a true cash balance. They can even pay the bills, by writing the checks for you to sign. This work will help you and it will help the girls handle their own bank accounts later.

And if they still complain (and they will), give them sympathy instead of a lecture. "Of course you want more clothes. We'd love to be able to give them to you." And then ask them what they'd get if they suddenly had a million dollars.

In turn, tell them what you'd like to buy with your million dollars. By sharing dreams, the three of you will become conversational equals -- and you'll find out what birthday and holiday presents would be best for the girls.

A yen for camp -- and all other wishes -- deserve sympathy too. The girls have the right to gripe and they'll need to gripe less if they know that you and their dad are listening to them.

No matter what measures you try, there will be some backchat, as there is in any family. As wonderful as they are, teen-agers are a tad self-centered.

They'll have more empathy if they do some volunteer work when they're with you, like making soup for your town's soup kitchen or tutoring a needy child.

If you think they still fuss more than most teen-agers -- and they probably don't -- it's really not a money problem, but a divorce problem. A residue of anger and disappointment is inevitable on all sides when a marriage breaks up, but don't let it center on money.

Love and understanding are the currency that count. Questions may be sent to P.O. Box 15310, Washington, D.C. 20003.