Don't Talk to Strangers

I took my kids to the park this morning. (I wonder how many of my blog posts started with that very line.)
Amelia was happy on the play structure, but Cole wanted to play in a small clump of trees where some older kids were playing. He would be out of my eyesight, so I reminded him, "Don't talk to strangers."
You know. The advice we all give almost reflexively and without thought to how general it is.

A half hour later, both my kids had migrated to a very tall slide at the top of the playground. Cole climbed up. Amelia followed. A three-year-old boy followed both of them. Cole didn't want to go down the slide right away, so he moved over and the little boy went down in front of him. Cole sat at the top of the slide, saw me watching and gave me a big thumbs-up sign.
I gave him a thumbs-up back (thinking that I was positively reinforcing the thoughtful act of allowing someone to go before oneself).
Then my son hollered across the playground, "I TOLD THAT STRANGER NOT TO TALK TO ME!!!!!"