Yes, there's even a day to celebrate kissing. In the context that I work in, kissing probably has somewhat different connotations from those that International Kissing Day celebrates, but nevertheless they are something that young children have an opinion about. They often hate them publicly, but crave them when unsure, anxious, about to go to sleep or need reassurance from loved ones and are away from peers. Kisses are given to say hello; say goodbye; say goodnight; and to say 'I love you' and all of these appear in picture books. Here is a collage of those in my library and as well as all those reasons mentioned they also cover the 'yucky' and the 'too many'.