Chocolate is made by grinding the seeds of the cacao tree into a sludge. Until about 500 years ago, this bitter chocolate was consumed only by people living in the area around present-day Mexico. However, the Spaniards who conquered Mexico brought it back to their country and it spread to Europe, as it was said to be energizing.
Eventually, sugar was added to the drink, and eventually milk was added to give it a mellower taste, or it was molded and made into chocolate bars.
In other words, chocolate was at first a kind of drink that adults took to cheer themselves up.