Kissing in young children, how to handle?
Young children kissing each other are just being affectionate and it's not something to discipline for if it makes you uncomfortable. Instead, it's a good time to have the conversation about personal boundaries (theirs and others) as well as appropriate ways to show affection that are universally accepted.
Neither of my kids were into kissing. My friends little boy ALWAYS wants to kiss and hug on Bub and he hates it with a passion. I told the little boy to stop one day after Bub had told him to stop a million times and the mom got mad at me. Oh well, no means no!