Käännös - Italia-Englanti - Il figlio non smise mai di mangiare.

why it is not used present perfect? (there is a "never" there)

A "never" does not always calls for the use of present perfect Oana.
We use "never" with simple present, simple past and many tenses other than present perfect. In this case what is being told is a completed event in the past, not something that still happens, therefore the correct tense is simple past.

Many thanks!! (I didn't contradict, I just try to understand)

I know verb tenses are tricky.
But as I always say, in English everything has a reason. Verb tenses are difficult in English, because we must use the correct tense for what we "want" to say. (A bit hard to explain)
A wrong choice of a tense may lead to a misunderstanding.