If were a one time incident, I’d ignore it and just keep walking. If those same kids were hanging around the next time I was having a walk and started it up again, I’d call the cops and just ask if they can swing by and have a chat with them about shouting insults and threats at people walking by.
The camera idea is good, too- get a good zoomed it digital pic of the little bastards and bring it in to the school and find out who they are. It’s bullshit that they should get away with making you feel unsafe on your walks.