It's the first day of kindergarten, everyone's feeling a little nervous. Especially during playtime. No-one knows each other and this is everyone's first social interactions with children their age. And maybe there's a few arguments in the yard. But what's the teacher going to do, huh?
Honestly, Just have a fight with everyone in that form that kindergarteners have. You know, "I was here first," "you're not my friend any more (even though it's the first day)," 'You're not invited to my birthday party." and "I'm telling off you." And so on. Also, most importantly, don't take anything lightly, take it all to heart and let the little child part of yourself respond.