Wisconsin Tattoo Laws
No one may tattoo children except doctors doing so in the course of their medical practice: “(2) Subject to sub. (3), any person who tattoos or offers to tattoo a child is subject to a Class D forfeiture (3).” (3) Subsection (2) does not prohibit a physician from tattooing or offering to tattoo a child in the course of professional practice.[44]
No one under the age of 18 may be tattooed, regardless of parental consent.
http://en.wikipedia.org/wiki/Legal_status_of_tattooing_in_the_United_States#Wisconsin