The limitation of child labor is another factor to consider as well. (But then, we are not getting paid... so :? )
Actually not as it would not be considered child labour. Child labour is when a child is working in a sweat shop making footballs, carpets or whatever, and are denied the chance of an education. Also work that put's the kid in danger, like construction, operating machinery or vehicles is forbidden, but there is no problem doing ordinary gardening work, administrative work or such.
Any labour performed by a child that is done voluntarely, and does not put the child to danger, with a decent salary is legal. Think paper boys, pop artists, actors etc...
Therefore, legally, hiring a person below 18 is OK from that point, and with the parents written permission there would be no problem at all, and parents are allowed to sign contracts on behalf of their children.
As I have understood though it's more about being sure there is a certain level of maturity in the business, and Daniel shows maturity (most of the time

)