First we need to tackle the difference between 'Il est' vs. 'C'est'. Although not a huge grammatical error if chosen incorrectly, it looks impressive to examiners when a student can differentiate between the two. Since 'it is shocking that' is a subordinate clause (does not make sense on it's own, needs to be attached to a main clause), we would use 'il est' (this is a rule which can be learnt). Therefore, the first part would be: 'il est choquant que'. To translate 'vulnerable adults are', we do not use the indicative form of the present tense, instead we need the subjunctive. The subjunctive is a mood (not a tense) used to express doubt, possibility, judgement and emotion. Sometimes, there are set expressions which take the subjunctive such as 'il faut que' and 'je doute que' (these, again, can be learnt). Since judgement is being expressed i.e. 'it is shocking', this means that it is not a matter of certainty and cannot be taken as a definite fact, therefore the subjunctive is used. We conjugate the third person plural of être as 'soient'. Thus, the translation would be 'Il est choquant que les adolescents vulnérables soient punis (remember agreement!) si sévèrement.'