The police don't have the right to come onto your property and tell people to leave just because there are a lot of people present. It doesn't make any difference if you haven't specifically invited a crowd, as long as you permit it. As soon as YOU don't want the people there, YOU can demand that they leave. You can even have the police make that demand on YOUR behalf.
If the people refuse to leave, they can be cited or arrested. But the cops can't come onto your property and cite or arrest people that you have permitted to enter.
Amazing how many people have forgotten
Amendment I.Particularly the (armchair) drug warriors and the law and order uber alles typesCongress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the Government for a redress of grievances.
I think one thing that would help us all more understand the situation is if we knew the configuration of the K-Mart, Sonic and the parking lot. If the lot is large, and the Sonic is 100, 150 yards away from the K-Mart, then we have two separate issues in my opinion. It would be obvious as to who was at Sonic, and who was just hanging around in the parking lot that adjoins the two places. The letter that was written to the paper by a neighbor says the kids were "all over" the parking lot. Assuming what she says is true, then its likely that any legitimate patron of K-Mart stayed away from there on Saturday nights. Like I have said before, the cops really had no right to bother anyone at Sonic unless they had gotten a specific complaint from Sonic about a specific person or people.