to train them to the fence, put them into a small yard first with a wire at nose height running along the inside of a conventional fence. Keep them here until you know they have zapped themselves plenty of times and know to keep well clear of the fence. It doesnt usually take them long to be trained, but you dont want to start training them with just the electric wire because a lot of them will charge forward through the wire when they get their first zap - that is why you use it in conjunction with a normal fence first.
now, the kids are going to be a whole lot more difficult to keep in with three wires, you may even need four. Standard sized adults on the other hand, I have successfully kept in with 2 strands of very hot wire. So adults might be a better bet for you.
The other thing you might want to think of, is if you have a couple of portable panels you could make a small enclosure for them and move it along the tree line every few days till they've eaten it all. More work, I know, but just a thought.