Most of us had an answer to this question while in grade school. For some of us, our dreams have come true. I always wanted to be a mad scientist, and I kinda' am.
Some of you are still on their way towards their goal: good luck!
Some of you have changed your minds as you 'grew up'. Many went into professions far more satisfying than their original choices
Others have been sidetracked due to unavoidable life events.
I that movie Best Little Whorehouse in Texas, Madame Mona laments the fact that she couldn't become a ballerina: "Me jumpin' up and down? I'd black both my eyes!".
The reason why this thread is relevant is that "I want to be a high priced callgirl" was seldom an answer to this question in grade school for you ladies.