Confusing Possessives

With names of holidays, do you use an apostrophe? If so, do you use singular possessive or plural possessive?

Examples:
Mother’s Day vs.
Mothers’ Day vs.
Mothers Day

Secretary's Day vs.
Secretaries' Day vs.
Secretaries Day

Boss’s Day vs.
Bosses' Day vs.
Bosses Day

Do you think of each mother, secretary, or boss as “owning” the day (Mother's Day, Secretary's Day, Boss's Day)? Or do you think of them as a group “owning” the day (Mothers' Day, Secretaries’ Day, Bosses’ Day)? Or do you think of the words as plural adjectives (Mothers Day, Secretaries Day, Bosses Day)?

There is no right or wrong answer. However, The Chicago Manual of Style lists the following holidays as singular possessives: Mother’s Day, Father’s Day, New Year’s Eve, New Year’s Day. Plural possessive is used for Presidents’ Day because it is in honor of both President Washington and President Lincoln. I don't think the verdict is in yet about Secretary’s/Secretaries’/Secretaries Day or Boss’s/Bosses’/Bosses Day. My guess is that the plural possessive form (Secretaries' Day/Bosses' Day) will eventually win.

What would we do if we had a Children’s Day holiday? Because Children is an irregular plural (not formed by adding an s or es), we would have to use the apostrophe in the title (Children's Day) because there is no such word as Childrens.