It's a great idea. I did that when I was a child.
$10/hour is enough for even my pampered kids. It's a great bootcamp to teach the value of an education and how much better it is than hard labor.
That can be successful but it depends on the location and the crop. IF the farmer is very near a metropolitan area and IF the crop is not fragile it can work. But you've got to have a LOT of insurance, plus parking, porta-pottys and LOTS of supervision to make sure the "customer" doesn't destroy more than he picks and pays for. Most farmers have found it's more work than it's worth.
Please see my post on farm labor further down the thread.