All minors (under 18 years) must have either a Blue SCA Membership Card or a completed Minor Waiver form.
The Midrealm (Kingdom where we're located) offers two Minor Waiver forms:
and
If You're bringing a kid who is not legally yours. . .
You MUST have a Medical Authorization Form filled out and signed by the parent/legal guardian of the child/ren.
In Michigan, it does NOT HAVE TO BE NOTORIZED but IT DOES NEED to be witnessed. And you need the waiver/their blue card.
More information: Midrealm Minister of Youth Website