The correct option is A No change
Some verbs take two objects, a direct object and an indirect object. The indirect object is the recipient of the direct object, or an otherwise affected participant in the event. The direct object answers the question 'what?' and the indirect object answers the question 'for whom?'
In
the given sentence, "her niece and nephew" is the indirect object and "their favourite toys" is the
direct object. The former is placed before the latter, hence option A is incorrect.
Option B is incorrect because the indirect object here is placed after the direct.
Option C is incorrect because the object "toys" has
taken the place of the verb (bought) and vice versa.
Option D is incorrect
because the sentence has changed in meaning (also, the pronoun 'her' has been placed before the noun it would replace 'aunt').