I'd definitely be making sure that they ALL understand that they aren't to be bringing ANY animals with them at all....that they need to be ON time (or early) and dressed properly...and any other thing that you need to address.
Oh, and IF it were my farm, I would have made darn sure that a JUDGE ordered them to true community service on my farm. That way little spoiled rich boy wouldn't have been able to buy himself out of hard labor.
Maybe you should tell them that they wouldn't have been so lucky had they done this on some other farms that you know.
A couple years ago, my then 13 year old son had the responsibility of filling the water trough for three steers and two heifers. It was to be filled daily with cold water because it was hot.
I noticed them lingering at the barn, and asked my son if he had filled the water. He said yes.
On a hunch, I walked out there, and guess what? no water.
I was really really PO'd. Animals do NOT do without fresh water at my house and my children in no way will EVER lie to my face and get away with it.
I handed him a quart jar. He got to fill that 60 gallon trough with a quart jar and five thirsty cattle drinking it as fast as he poured it. He walked approx 20 feet for every jar of water. Took him HOURS.
He does his chores on time now, and to my knowledge has not lied since.
Am I mean? Yup.
Do I care? nope.
Lol, you know the saying about a woman scorned..........
I did the EXACT same thing to my oldest boy when he lied to me out watering the outside dog. He had to fill a 5 gallon bucket with a cup by walking back and forth to the kitchen sink (about 75 feet).