If you're talking to one of your adult friends and talking in the past tense, you can add some words in front of the sentences so it can make a bit more sense.
Ex. "When you were a kid, what did you want to be when you grew up?"
For the first sentence, I would talk to a child under the age of 18. I would reword it a little.
Ex. "What do you want to be when you grow up?"