I think it all started when we taught Annie how to give Butterfly Kisses. Now when it is bed time, and I am tucking her in bed, Annie looks at me and says, "I'm going to give you my Special Kisses." She proceeds to give me a Butterfly Kiss, an Eskimo Kiss (rub noses), a Pig Kiss (snort on my cheek), and then she will make up any number of other "kisses," usually blowing somewhere on my face. She always names them, although after she came up with the Pig Kiss, the names are usually gibberish ("The Googookashalsha Kiss").
Maddie has taken up the tradition. By the time I turn off their bedroom light, I've had at least 10 different kinds of kisses, each new one named.
In their creativity, I have had to draw the line at licking ("Dog Kiss") and slobber of any kind.