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Of course, you're delighted your baby has found "the one." But if the prospect of paying for your child's special day has you hearing wedding blues instead of bells, it's no wonder.

Weddings are costly affairs, running $31,213 on average in 2014, according to TheKnot.com’s annual Real Weddings Survey. While that number is certainly skewed higher by the extravagant spenders out there—we're looking at you, bridezillas—it's still scarily large.

Scary especially for the bride's parents, who contribute 43% of the total wedding budget, amounting to about $13,422 on average.

Don't have such a large sum put aside for your kid's nuptials? Don't spend the big day worrying about impending bills or, worse, going into debt. Here's how to gently break it to your child that you can only give so much.

YOU SAY: "I'm so glad you and James could come over for lunch. I want to hear all of your wedding ideas."

Because this conversation can be difficult and you don't want to disappoint your child, you may be tempted to put it off. But if you wait too long into the planning to state your intentions, the bride and groom could have already made (costly) assumptions.

So as soon as the celebration around the engagement dies down a bit—and before the planning starts to get underway—schedule a time to sit down privately with the couple to talk about what you can contribute.

Don't leave the groom out! "The couple needs to hear it together first-hand since a wedding is all joint decisions and both need to know the budget," says protocol and etiquette consultant Nancy R. Mitchell.

YOU SAY: "Your father and I want to help you both pay for the wedding, so we've set aside $XX,XXX for you to use to cover costs."

Once you and your spouse have run the numbers to come up with a figure you can responsibly give without endangering your own savings goals, let your child know exactly what that amount is.

You might be tempted to simply say that you'll cover, say, the catering or venue costs rather than naming a number. But that's a bad idea: "Without clear budget guidelines, your child will be writing checks without knowing what the balance actually is," says etiquette expert Diane Gottsman. And that could put both of you in hot water when the bills come in.

YOU SAY: "We would love to be able to help out more, but we're still paying your brother's college tuition and helping your grandparents with medical bills."

If you can't afford to help at all or the amount you can give is less than what you or your child had hoped for, explain why.

You don't need to go in too much detail—your child doesn't need to know the exact amount in your bank account or the total cost of the mortgage. But you can remind him or her gently of your current money obligations, says Gottsman, who owns The Protocol School of Texas.

This way they understand where the number is coming from and can truly appreciate your generosity.

YOU SAY: "Of course, you can always count on us to make centerpieces or call venues, or anything else you need."

Remind your child that though your ability to help with money is limited, you're willing to put unlimited (or at least less limited!) time and effort into helping make the big day special.

Wedding planning is stressful, and your child may need a supporting hand when the to-do list runs down past her knee. Let her know that you'll always be available for a venting session or to make 500 packets of Jordan almonds at the last minute.

YOU SAY: "What are your plans for any expenses that go above what your father and I can help out with?"

As a parent, you don't want to see your child's marriage start in debt. But nearly half of couples do end up spending above their wedding budgets.

So some of the best help you can provide is to help your child make concessions that will help them stay within their means.

"Always pressure them to stay in budget and scale back," says Minneapolis-area certified financial planner Sophia Bera.

"If they do decide to spend more than they have on the wedding, and it's only a few thousand dollars over, I'd recommend dipping into their emergency savings account," she adds.

If it's more than a few grand, she suggests putting the costs on to a 0% credit card (Money recommends Chase Slate, which charges no interest for the first 15 months). "But then they need to build into their new household budget a method to pay it off quickest," Bera says.

More on wedding planning from Money.com:

10 Most Expensive Places to Get Married

8 Ways to Throw a Memorable Wedding for Less

Say Yes to a Cheaper Wedding Dress