People Kissing?

The other day, Judah was giving me some sweet kisses on the face.
"I'm giving you baby kisses, Mama."
"Ooooh, thank you, Judah. I like these! What do big kid kisses look like?"
Judah proceeds to give me a kiss on the lips. Then, "Do you want a people kiss?" (Judah calls any adult a 'people'.)
"What does a people kiss look like, Judah?"
"We open our mouths."

I passed.

Where does a three year old get this? Will and I are careful not to turn on adult shows until after our kids go to bed. Are our babysitters making out in front of them? Should I even bother figuring this out???