Thank you for your question!
The difference here lies in the correct structure for expressing this idea in French, as well as how certain verbs (like demander) interact with objects. Let me explain:
Why "J'ai demandé mes parents pour un livre" is Incorrect
Verb Usage with Direct and Indirect Objects:
In French, the verb demander (to ask) requires a direct object (the thing being asked for) and an indirect object (the person being asked). The correct structure is:
demander [something] à [someone]
Example:
J'ai demandé un livre à mes parents. = "I asked my parents for a book."
In your first attempt, "mes parents" was treated as the direct object, but this isn’t how demander works. Instead, the thing you are asking for (e.g., "un livre") should be the direct object, and the person you are asking (e.g., "mes parents") is the indirect object introduced by à.
Why "à" and Not "pour"?
"À" is used because the French construction "demander à quelqu'un" directly means "to ask someone." It introduces the person receiving the request.
"Pour" would mean "for," which suggests you're asking on behalf of someone or for their benefit—not directly addressing them with the request.
Example:
Je demande un livre pour toi. = "I am asking for a book for you."
Correct Sentence:
J'ai demandé un livre à mes parents.
un livre = direct object (the thing you asked for)
à mes parents = indirect object (the people you asked)
I hope this clears things up! Let me know if you have more questions.
