Generally, a passive-voice sentence is one where the direct object replaces the subject, an action verb is replaced by a perfect-tense construction, and the subject is put into a prepositional phrase.
The dog bit the postman. (active voice)
The postman was bitten by the dog. (passive voice)
Your sentence does not contain an action verb or direct object. You could say, "Malaria is affecting both her children," but this is not passive voice.