Yes, talk to your [sic: they are each their own person; you are their guardian, not their owner, ffs] children and teenagers about emotional literacy, privacy, and social boundaries.
No, do not restrict their communication options.
All that does is penalise the most vulnerable. I would most likely not have survived my childhood without other people online.
Yes, any tool can bring harm and risks etc. Listen to them, by being someone they can trust will NOT freak out when they make a mistake.
https://www.youtube.com/watch?v=2yVJffNplJc