What about "The child cannot be seen as a patient." (It was marked as wrong.)
I am not sure how to interpret the correct answer. (Is the child missing from the hospital records?)
My first interpretation of this is "The child doesn't seem to be sick."
The primary meaning of "mgonjwa" is "a sick person". A sick person may or may not be a patient, although the word "mgonjwa" is used for "patient" in Swahili. In translating of course one has to look at the context. With no context, what I see word-for-word is "child does-not-seem like he-is sick (person)".