McDonald's debuted the Happy Meal nearly 40 years ago. Here's how it's changed over the years

Few things are more iconic than a McDonald's Happy Meal. The bright red box with its golden handles has become a fast food staple since it was first introduced nearly 40 years ago.

However, the Happy Meal fell out of fashion with some advertising partners in the mid-2000's. A combination of rising childhood obesity rates and concern over calorie-laden children's meals at fast food restaurants led companies like Disney to part ways with the brand.

McDonald's has tinkered with its Happy Meal, overhauling the food inside the box and serving up healthier food options for kids. The Golden Arches now offers selections that are lower in calories, sodium, saturated fat and sugar.

These changes led Disney to rekindle its relationship with McDonald's in February, more than a decade after it severed ties with the burger brand.

This wasn't the first time McDonald's made major changes to its iconic Happy Meal. Here's a look at how McDonald's Happy Meals have evolved since 1979:

The classic kids' meal started as a gimmick, a way to lure in parents with small children for an easy-to-order lunch or dinner.

The Happy Meal let kids choose what they wanted to eat, giving them a sense of autonomy, and helped McDonald's brand itself as family-friendly fare.

This first iteration of the Happy Meal was the Circus Wagon box, which came with either a cheeseburger or hamburger as well as fries, cookies, a drink and a toy.

Chicken McNuggets were added a few years later as an alternative to red meat. In the '80s, diners sought to decrease the amount of fat and cholesterol they consumed and demand increased for leaner meats and poultry.

Truth be told, the Happy Meal isn't most well-known for its food. Instead, it's often the trinkets inside that have gained the most notoriety. Ask anyone who grew up eating McDonald's and they can instantly tell you what the most coveted Happy Meal toy of their generation was.

Early on the toys included in the Happy Meal were little trinkets — stencils, puzzle locks and spinning tops. However, those toys got an upgrade over the years due to several strategic partnerships.

The "Star Trek" meal was the first of McDonald's major film partnerships. Television ads enticed parents to bring their kids into their local McDonald's to get a kids' meal with a special "Star Trek prize."

This trend continued as McDonald's teamed with Disney and Mattel's Hot Wheels and Barbie to its list of partners.

Kids love to collect. Their need to accumulate every iteration of their favorite show, movie or character has been and continues to be one of the strangest drivers of growth in the toy industry. Offering up beloved characters from the House of Mouse and already popular toy properties was a way to lure in families multiple times over the course of the limited release of a themed meal.

So, when McDonald's hopped on the Ty's Beanie Baby trend in the '90s, it was no surprise its customers reacted with such fervor. In 1997, McDonald's began handing out Teenie Beanie Babies in its Happy Meal and soon found lines of people out the door hoping to get their hands on the collectible. These miniature stuffed bears can still be found on eBay with price tags between $500 and $7,000.

Not long after the Teenie Beanie Babies craze, McDonald's found itself at the center of a growing debate. Childhood obesity rates were rising and there were concerns about calorie-laden kids' meals at fast food chains. Some even called for toys to be banned from meals meant for kids.

McDonald's had already begun adding to its kids' meal offerings. It introduced milk as an option in the late 1980s. But by 2004, it opted to serve reduced fat milk, in regular and chocolate flavors, and apple juice as alternatives to sugary soft drinks. Cookies were swapped out for apple slices. Eventually, Gogurt yogurt tubes would also become an option.

But critics weren't appeased, even when the chain added nutritional information to its Happy Meal packaging in 2005.

More recently, McDonald's revamped its selections so that they are now lower in calories, sodium, saturated fat and sugar. This meant ditching cheeseburgers and chocolate milk from the kids' menu.

While these items are still available for purchase, McDonald's will not list them on the menu, thus making it less likely that these items will be ordered, it said.

This move brought Disney back into the fold in February, just in time for the entertainment giant to promote the highly anticipated "Incredibles 2," which is due out in June.

"The Incredibles" has become a cult favorite, especially among millennials, who are starting to have families of their own and could be drawn into McDonald's for these promotions.