Do not employ persons under the age of 18 to do work on your sites. Period.

First, someone under 18 is not going to be bound by a contract. [good legal reason to stay away from under 18 employees]

Second, you are very likely exposing the under-18 designer to pornography and very likely committing a crime by doing so [another very good legal reason not to hire under 18 employees]

Third, they are just not reliable!