In my ward they like to "spotlight" one of the children during Primary by asking them a series of questions. One of my favorite questions they ask is "what do you want to be when you grow up?" Not to be a Debbie-downer or anything but usually after the child answers I think "yeah, like that's going to happen." I just know, from personal experience, that you usually need to live a little before you can truly decide what you want to be when you grow up.
For example, when I was 7 or so I wanted to be an astronaut. You know, fly to the moon, walk around, the whole shebang. Then I discovered I more or less hated science, so that went out the window.
Then, I wanted to be a zoologist and work with orangutans. But again, science was involved and the more exposure I had to animals the more I determined I'm not a big fan of them.
Shortly after I decided that what I would really enjoy being was a mailman (I know, big aspirations, right?). I thought it would be just swell driving around, whistling, handing people their mail. But again, reality hit. I hate driving and I can't find locations to save my life.
Well, years and years, and a lot of schooling later here I am. Neither an astronaut, a zoologist, nor a mailman, but a social worker. And what little kid aspires to that?