This guest post is from Naomi Mannino. Naomi is a freelance consumer personal finance and health journalist who reports on health, medical and personal finance news and how it will affect your life today. You can follow Naomi on Twitter @naomimannino.

My 19-year-old daughter came to me sobbing and wanting to borrow $20 for a concert because she didn’t have any money. I simply said, “Nope.” That made the sobbing worse.

Now, before you accuse me of being cheap and mean, know that she works at McDonald’s about 15 to 20 hours per week (more in the summer) and has for many months. She also has a habit of completely spending every penny of every paycheck, even though her direct-deposit paycheck splits the money into a checking and a savings account. My husband and I insist she pays us first for her portion of the car insurance and her smartphone service, but then she spends the rest from both accounts as she pleases on gas for her car, clothes, nails, cosmetics and — most of all — fast food.

I have found that you can set up bank accounts with savings, model good spending (and eating) behavior and show and tell teenagers what to do but you can’t make them save the money or not spend money they earn. So through the sobbing, I tried to be helpful and said, “Let’s sit down and look at your account online and see where you spent all your money. Maybe you can change your spending so you have enough for something unexpected next time.”

Time to do the math

We opened up that month’s transactions and faced page upon page of $1 to $5 transactions at Taco Bell, McDonald’s, gas stations, Dunkin’ Donuts, and many larger transactions from Starbucks and Panera Bread. “I just bought a drink, that’s all,” my daughter whined. I also heard, “It was $1 nugget day.” The grand monthly total for just the junk food came to $180. And she had hardly been eating anything at home. (Don’t get me started on the nutrition aspect of this problem because I am a mom who loves to cook five to six nights per week.) She was stunned at how much money her junk food cost her.

She was dismayed to learn that she was giving a large percentage of her paycheck back to McDonald’s (despite a discount), but in the end, I didn’t get the sense that she really cared what I had to say or was interested in changing her behavior because she stormed away calling me “mean” and “cheap” when I wouldn’t give her the $20 for the concert.

What if they are paying their needs first? Should you have a say in the rest?

My younger teenage daughter (age 17) works at Wendy’s, and she also pays her smartphone service and a portion of her car insurance from every paycheck. She spends more on clothes, shoes and accessories than her fast-food-loving sister, but her fast-food bill still came to a whopping $120 per month with an additional $40 at IHOP and Applebee’s. And, although she has never asked me for money, she’s occasionally felt the pain of spending her whole paycheck, though not enough to make her reconsider her spending.

My son is turning 16 next month and does not have a job yet or a car yet, but he does have a small allowance of $15 per week, which goes straight to the corner gas station for a huge soda and a bunch of candy from Dollar General almost every day. How can I stop him? It’s his allowance.

Letting them learn the hard way

Given what’s happened to my kids, I feel like having them get jobs has not taught them what I was hoping, which was that fast-food, minimum-wage jobs stink (and you should go to college) and to learn to budget the money they earn for things they need and want plus to save a portion for an emergency. Instead it has taught them to spend every cent they have on whatever they want.

I think of all the reasons that their spending habits could be our fault:

  • Our expenses every month equaled only a little less than we brought in for so many years.
  • We said no to things because “we can’t afford it.”
  • Could it be our fault because I never use credit cards and wait to purchase things I both need and want until I have enough cash?
  • Do they hate my couponing?

My kids seem to want what they want when they want it. My daughters’ friends also make car payments and pay for their phones and also seem to be equally fast-food addicted. Maybe it’s the company they keep? (Beggars can’t be choosers when it comes to jobs for teens in our town.)

Every day, they drive and pick each other up and head straight to the nearest fast food. My son waits anxiously for his sisters to come home and drive him for his fix. I have learned that nagging and pointing out truths about a fast-food diet or making snide remarks about their spending, being broke or fast-food calorie consumption definitely does not work.

Pick your battles

It’s sad for me to watch my kids squander their money, but I think they have to learn their own hard lessons, and I must stick to my guns. If they run out of money, I don’t give more. Beyond the money, it hurts me to see them enslaved by the scientists behind the food industry, as I read about in Michael Moss’s new book, “Salt Sugar Fat: How the Food Giants Hooked Us.” Morgan Spurlock of “Super-Size Me” fame also discovered the addictive quality of fast-food in his famous documentary.

I just have to pick my battles, as they say. When it comes to teenagers, there are so many worse things they could be spending their money on, such as alcohol, cigarettes and drugs, and these vices are non-negotiable with known bitter consequences in our family.

I hope this phase will pass sooner rather than later. I know my kids will wish they had more money saved one day for a car, traveling or for college living expenses. But I am secretly saving the money they give me for their car insurance and smartphone payments as their savings. (Shhh! Don’t tell them!)

Do your teenagers spend more on fast food than you ever thought possible? What do you do about it?