When I was really little, I had trouble answering that question. I understood that they meant "to earn money", but I thought that when a girl grew up, she became a housewife and the husband earned the money
When I figured out that I *had* to put a marketable career down, I said I wanted to own either a petshop so I could play with all the animals, or a bookstore so I could read all the books. (that would be second grade or so)
Around 6th grade I started wanting to actually help people, so I changed to wanting to be a vet (since I liked animals better than people). And then to a nurse.
In 9th grade, my Biology teacher focused on all the plant chapters, and barely touched on the animals. I discovered that I hate science projects, hate science reports, and can't stand subjects that rely on a lot of memorization. After a year and a half of soul-searching, I settled on teaching high school math.
When that didn't work out, I became a cam-model, and started debating between programming and accounting. I went with accounting because I won't have to worry about learning a new language every 10 years, and a new operating system every 3 years.