Why are you considering your parents as some sort of special case? Your question is equally appropriate regarding anyone of any age.

In any case, I would advise everyone (including your parents) to have a safe word/phrase such that everyone knows that if that word or phrase is not used in a important communication, then it isn't really from them.

Beyond that, the usual safety rules apply: never click on links, never talk to businesses if they call you (look up their number and call them back if it seems important), etc.