According to my research, the only way for Maggie to drink without Miko caring as a cop would mean the show has to take place in either
1.)
Connecticut where the drinking age is 21 unless (1) a person over age eighteen who is an employee or permit holder under section 30-90a and who possesses alcoholic liquor in the course of such person's employment or business, (2) a minor who possesses alcoholic liquor on the order of a practicing physician, or
(3) a minor who possesses alcoholic liquor while accompanied by a parent, guardian or spouse of the minor, who has attained the age of twenty-one. Nothing in this subsection shall be construed to burden a person's exercise of religion under section 3 of article first of the Constitution of the state in violation of subsection (a) of section 52-571b.
2.
Louisiana - 21 with the exception of when a person under twenty-one years of age is accompanied by a parent, spouse, or legal guardian twenty-one years of age or older
OR In a private residence, which shall include a residential dwelling and up to twenty contiguous acres, on which the dwelling is located, owned by the same person who owns the dwelling.
3.
Maryland - which is 21, however anyone can drink when parents, spouses, teachers are present.
4.
Ohio - 21, however, anyone can drink with parents or legal-age spouse present.
And possibly Wisconsin being the same as Maryland/Ohio.
I guess Maggie would count as the guardian of age?
But illegally, they could live anywhere. Or like it was mentioned, we're just meant to believe they have their own rules in a fictional town.
