I'm bothered by ANYONE on my property that doesn't have express permission to be there. We actually have a 6 ft privacy fence and a lock on the inside of our gate so even the meter reader can't get in. If I could keep people out of our front yard I would. People, especially kids, coming unsupervised onto a property with animals--especially large dogs and/or livestock--are a liability issue. Heck, a few species of livestock can kill or severely injure an adult without intending to, much of less a child. Also, if the OP's fence in not in great shape the kids could hurt themselves hopping it, which could be another liability issue. Aside from all that it's extremely rude, IMHO, to hop people's fences without asking or hike their property without permission, I don't care if you have 1/4 acre or a 100 acres.