Hello francesco, hello everyone
The topic of parental controls is a subject the Gnome team are actively getting into:
It will be a while before they bring a solution, but it's good to know that it is on their "to-do" list. 
We may see it appear later in Ubuntu-Mate..., as @Wimpy has previously said he would like to see Ubuntu-Mate become more children-friendly.
Let's hope the Gnome solution can be easily ported to Ubuntu-Mate. 