A friend of mine had a home day care center with a large grassy front yard for the children to play. It was not fenced. No need, she had two border collies. If the little tikes got anywhere near the edge of the yard, the dogs would “herd” them back. All day long, non-stop, these dogs ran back and forth, dashing toward any child that moved in the direction of the sidewalk, and zig-zagging back and forth directing the kid in the proper direction. Strangely, the children were not afraid but seemed to sense the dogs were “protecting” them and never tried to run beyond them.
My husband witnessed the same type of thing at a clients house. He said it was amazing how they kept the kids corralled and the kids didn’t even seem to notice.