As most children do, Theo gets kissed when he has a boo-boo. One day he started returning the favor. He started kissing my boo-boos, and even the cats' boo-boos, although they don't have any so he was really just making it up.
Once in a while he got confused and thought my beauty marks were boo-boos, and so he'd kiss those too! Every time he did that, I corrected him of course, and he would repeat -- "booty mark?" I'd tell him "yes, that's a beauty mark," and after a while, he got the concept of what a beauty mark is.
Now, he purposefully kisses my beauty marks! He'll find one, say "look, mommy, booty mark! Kiss!" and kiss it. I have a ton of them, and he finds them all. He'll lift my shirt and get to the ones on my belly, he'll find them on my legs... he's such a sweetie pie! In the morning he wakes up and comes into our bed, full of hugs and beauty mark kisses.