Happy birthday, Happy Meal. The little box with the signature arches-as-handles is turning 40 this year, and McDonald’s is celebrating with a nostalgia-triggering revival of some of the most popular toys to have been included in the kid-targeted package over the decades.

Starting Thursday, the fast-food giant is including with its Happy Meals one of 17 throwback toys. There are 1980s-era “McNugget Buddies” decked out as cowboys and mail carriers, a 1997 Patti the Platypus Beanie Baby, a Power Ranger from 1995 and a 2013 Hello Kitty doll.

But it’s not those little bits of shiny plastic alone — or even the meal itself, usually a burger or some nuggets and pint-size fries — that explains the Happy Meal’s success, which has come despite years of controversy over its effect on kids’ diets. To understand its longevity and appeal, look no further than the quote the company supplied in a news release announcing its special anniversary offerings. “This iconic red box creates lasting memories for billions of families annually across the world,” Steve Easterbrook, the former McDonald’s chief executive, said in the statement. (His words were written, obviously, before he was forced out after an affair with an employee.)

McDonald’s has been selling these “lasting memories,” along with its burgers and fries, for decades to both children and their parents.

“Their marketing position is that if you love your child, you’ll take them” to McDonald’s, says Jennifer Harris, director of marketing initiatives at the University of Connecticut’s Rudd Center for Food Policy and Obesity.

John Stanton, a professor of food marketing at St. Joseph’s University, says McDonald’s is following a long tradition of American advertisers. “Charles Revson of Revlon used to say, ‘In the factories, we make cosmetics, but at counters, we sell hope.’ ” he says. “McDonald’s is saying ‘Yeah, there’s this stuff in this box, but this experience is going to make you feel good — happy.’ ”

The fast-food chain’s anniversary campaign is a way to appeal not just to kids but also to their parents, many of whom grew up eating Happy Meals. Chances are, the mom or dad wheeling that minivan up to the drive-through window remembers getting, or at least coveting, one of the blast-from-the-past toys themselves. “If you had a positive experience there, you’re more likely to take your children,” Harris says.

To wit: another quote McDonald’s released as part of its anniversary campaign. The company did not make any executives available for an interview, but Colin Mitchell, the company’s senior vice president for global marketing, said in the release, “Parents tell us how fondly they recall their favorite toys. So, unboxing the Surprise Happy Meal together creates a real moment of bonding with their children. We hope these toys are something that they will treasure and remember.”

For parents, particularly working ones who might not have hours of time with their children, the proposition of spending around $3 for a “moment of bonding” is a pretty good one. Stanton says he has been in on focus groups that show mothers who work outside the home are anxious to make the most of whatever time they have with their kids. “They have this sense that they have to work hard at making a wonderful experience,” he says. 

So it’s obvious that much of the Happy Meal’s appeal isn’t just about sustenance but also contentedness. Still, in the course of its 40-year history, the meal has also caused plenty of anxiety.

In 2002, two New York teenagers filed a class-action lawsuit claiming that the chain’s food, including Happy Meals, had contributed to their obesity. The case was eventually dismissed. Other legal challenges include a 2010 California lawsuit that sought to stop the company from giving away toys, which plaintiffs claimed were used to lure children into eating unhealthy food. That was ultimately tossed, too.

Even outside the courtroom, almost since the beginning, the product has been fingered as both a symbol and cause of childhood obesity. The city of San Francisco in 2011 imposed an ordinance banning fast-food restaurants from offering free toys. But the wily Golden Arches got around the rule by tacking on a 10-cent surcharge for the plaything.

In recent years, McDonald’s has stepped up efforts to make its kids’ offerings healthier. The meal had long included either a hamburger, cheeseburger or McNuggets, along with a side of fries and a small soda. In 2011, it added apple slices and shrank the serving size of fries to 1.1 ounces. In 2013, it removed soda as the default drink. Subsequent changes included lower-sugar juices, reformulating its chocolate milk and dropping cheeseburgers entirely. Last year, it announced new goals, promising that by 2022, more than half of Happy Meals would contain less than 650 mg sodium and fewer than 600 calories, with less than 10 percent of those coming from saturated fat and less than 10 percent from added sugar.

Sina Gallo, an assistant professor of nutrition at George Mason University, says there’s nothing wrong with children having an occasional Happy Meal, but that even with healthier options, the bigger danger is making them a regular part of a child’s diet — and worse, creating little eaters who grow up to be frequent fast-food consumers as grown-ups. “We know that setting up behaviors very young can lead them to continue those behaviors into adolescence and adulthood,” Gallo says. 

Research suggests that they’re not just a rare treat for many kids. According to the Centers for Disease Control and Prevention, in 2011–2012, just over one-third of children and adolescents ate fast food on a given day. And Harris notes that research shows parents are increasingly buying regular menu items for older children in addition to their Happy Meals.

Meanwhile, McDonald’s is taking pains to highlight the meals’ slimmed-down profile. The company notes it has served “more than 3.4 billion fruit, low-fat dairy and water options in the Happy Meal since 2013″ — though it also boasts that it serves a billion of the kids’ meals annually around the globe. And it notes that since it nixed advertising soda as part of the meal, there has been a 15 percent increase in customers opting for milk, water or juice.

In other words, while the Happy Meal might be celebrating its 40th birthday, it likely won’t be getting cake.

An earlier version of this story included a reference to a survey that did not meet The Washington Post’s standards. This post has been updated.

More from Voraciously: