I just want to know how old these middle school students are. Did you mean middle school students or high school students? If this happens among middle school students, I think it's too early for courtship. If this happens among high school students, it's somewhat reasonable (but not recommended).
I hope this will not happen to me. To deal with these young people with early dating, it's better to start with communicate and educate them early. They might not even know what love is. They might not have the social and interpersonal skills to handle it. They have boyfriends/girlfriends because they saw other people have boyfriends/girlfriends. They kiss each other because they should act in a way like other people should act on relationship. But they don't realize their relationship has nowhere to go and develop. Parents need to help them understand the responsibilities and concerns about premature dating.
I think the parents (50%), the society (40%) and the school (10%) should take the responsibility for it. Since parents are consistently supervision the grown of their children, they need to set rules and boundary for how to behave. The school is responsible for providing guideline and education to help them understand what is right, what is wrong. The society is the environment where the young people grown and influence from. Looking at the today's media which includes TV programs, movies, news paper, magazines and internet, you will understand why these middle school students kiss each other in front of people in the public place. They learned that from what they saw from the media.