My 3 year old knows about weirdos on the internet.
We watch kids YouTube together. I've never seen them in person but I've seen newspaper articles about scary fake Peppa videos and things, so we've chatted about how anybody can put videos up and some people are unkind, and want to frighten children. If she sees something scary, she knows to tell me about it, and how to report it to kids YouTube so they can take it down.
I think it's so useful. She knows from this that not everyone online is trustworthy, but that we can deal with it together, and things that might be upsetting can be taken down. When she's a teenager and has weirdos trying to groom her, as could well happen and happened to me, that lesson will be as innate as anything else she's learning at the age of 3. Not everyone online is trustworthy and Mum is always there to help.
As to 'it should be left to the parents', I'm sure you are aware not everyone has good parents. Not every parent will teach their child things like that and in some cases will do much worse, in which case good job to the school for having the NSPCC in to teach them how they should be being treated.
Interestingly we've also discussed that.
Yet I've had comments from children's centre staff, from her nursery teachers, on how confident & well adjusted she is.
Some children are more sensitive but all children deserve to be able to keep themselves safe.