Describe how these people are feeling, what's the matter with them?
Good, a bit more "natural" sentence would be:
The girl in the first picture has a flu, woman in the second picture has a headache and that man has a cough.
(He is too old to be a "boy", ok :D )
the girl has a flu . The girl has the flu.
the next girl has headache and the boy have a cough .
The next girl has a headache, and the boy has a cough.
Actually, Marycelestine ... No. It is NOT a "certain" flu, so you don't use "the". So, a flu, a cough, a headache.
I am sorry it is THE flu. I am a native speaker of English. Our rules don't always make sense, but that's how it is said.
... and 80% of the English speakers can't write their own language. Just saying.
Check this, how it SUPPOSED to be said, not how it is said. If too lazy, google the words "I have a flu" or "when you have a flu..."... Thanks.