Sometimes, it's the parents...
A couple of kids came around offering to clear some brush from my backyard for $20 each. They were about 16, and seemed to actually want to work, so I said okay. At the end of the day, the results were impressive, so I paid them $25 each and asked them to come back the next day and finish the job.
The next day, their parents showed up and threatened me with legal action for forcing their children to perform manual labor, and for allowing them to use 'dangerous' tools (i.e., axes, loppers, machetes, et cetera). It didn't matter to them that they volunteered, because I "... should have known that a child cannot enter into a contract without a parent's consent" (or something like that).
Then one of them told me that their labor was worth more than the $50 I had shelled out, and that if I gave the parents $50 more as 'compensation', they would drop the whole matter.
"Call my lawyer", I says.
Had to finish the job myself.