Very interesting question. But it does depend on what do you see as work, and what do you see as fun, which is entirely subjective. For example, you might have fun in your work, but it's still work - meaning, at the end of the month, you'll get an economic reward for your effort.
In terms of "fun", the reward that you get is maybe, a sense of accomplishment due to finishing a difficult/challenging task, such as playing a sport. But what happens when you work as a professional sports player? The lines are very blurry.
However, in terms of children, I do believe it is wise to let them know that facing their responsibilities head strong will allow them to have fun in the long term. Also, making chores fun, ends up being very beneficial in a long term view, for example; I've always liked sweeping the floor. And it is because of my grandma, just because of a phrase when I was little: "If you're doing something, do it good, because no matter how small do you think something is, maybe there's people out there living off of it."