Handcuffed Kindergarteners

Teaching kindergarten, I see a lot. A LOT! What I didn't think I would see is so many behavior problems. I expected the crying when parents left. I expected the "so and so doesn't want to be my friend." I was prepared for the "he took my pencil." I had ideas for those situations, but the behavior I see this year is something that almost scares me. I currently have one student on a behavior plan. A BEHAVIOR PLAN! A five year old on a behavior plan?! It still takes me by surprise sometimes. I feel so unprepared for this. I can't help but try and connect the dots and wonder if I would've had this innovation in place already, would the behavior still be this bad? Is this a here thing? Is this an everywhere thing? Is this a five year old thing? Is this a home thing? I'm not sure why having the answer to those questions would matter, but that's what runs through my head. I'm not a behavior specialist. I struggle at parenting most days, yet I'm expected to put this child on the right track with zero to no tools. What are your thoughts on behavior in kindergarten? The even bigger question, what is your take on punishment or consequences in kindergarten?