It's not just ONE talk, it's an ONGOING line of communication.
If their underwear or swim trunks cover it?
NO ONE touches it.
NO ONE should ask to see it - except for a Doctor with ME present.
it's NOT about a stranger - as evidenced here - more molestations are done by a known family member, sports coach, teacher, etc. this way - they can tell the victim that "their mom or dad won't believe them" or "It's our little secret".
Tell your son that NO ONE is allowed to touch his private parts..they are HIS private parts...COMMUNICATE with him on HIS level - not an adult level - tell him that NO adult should ask him, a child, to help him find a puppy.
No adult will be allowed to pick him up from school.
Set a password that is ONLY known to you guys - that wouldn't be obvious to someone else - like the name of his teddy bear - and if an adult were to come to somewhere and pick him up - he needs to ask "what's the password?" and if they don't know it - then he's NOT to go with them... you can use that later if you wish - but the gist is that this is NOT just ONE talk. It's an insert in many conversations.
GOOD LUCK!