Magical Guardian

This is a magical being who's in charge of a group of children, whether as a nanny, teacher, or some other form of custodian. Has some overlap with the Magical Nanny, but while a Magical Nanny is focused on improving family dynamics and behavior and may or may not be really magic, a Magical Guardian is really magic and may or may not do anything about behavior and family. They may instead use their powers for the more broad purpose of education, or even just for the pure sake of adventure. Having this character around allows children to get up to all kinds of impossible and wacky hijinks without audiences wondering where the parents are.

Such a character may be Inexplicably Awesome.

Film

 * Mary Poppins
 * Nanny McPhee

Literature

 * Susan Cooper's Over Sea, Under Stone, the first book in The Dark Is Rising series. While the Drew children are on holiday in Cornwall they're taken care of by their great uncle Merriman Lyon. He's a powerful magical being whose duty is to protect them from the forces of the Dark.
 * In the Alternate History Magitek novel Operation Chaos by Poul Anderson, Virginia is a witch with a cat familiar named Svartalf. When she and her husband go out to dinner and a show, Svartalf gets to babysit their child. Being that Svartalf is quite intelligent and responsible, as well as magical, it's not as neglectful as it seems. When.
 * The Cat In The Hat from Dr. Suess. All the tension in the story is will the children recover from the outlandish stuff before Mom and Dad find out what went on?
 * On the Discworld, Susan Sto-Helit works as a governess and later a schoolteacher. She's also the granddaughter of Death.
 * Bast from The Kane Chronicles.
 * The gecko/dog from I Am Number Four.

Live Action TV

 * Barney the Dinosaur

Western Animation

 * The Magic School Bus's Miss Frizzle, the former Trope Namer for Inexplicably Awesome.
 * A villainous example: Mother Mae Eye from Teen Titans forced herself on the heroes and even used mind-controlling pie to insure they obeyed her.
 * Another Teen Titans episode involved Raven escorting three child superheroes to a safehouse as their protector.