Throughout the film, Julia Roberts wears enormous ball gowns. On the set, her children hid underneath her skirt without anyone knowing. In between takes, Roberts had her children removed from the set because she was concerned about them hearing her "vile" dialogue as the Evil Queen.
Almost all of the unlikely seeming beauty treatments the Queen undergoes are actually real treatments you can get at spas all over the world. Among the real ones are: the bird poop paste, the chocolate (or clay, it's not clear which it is since it's brown) mask, the snake massage, the snail slime, the maggots and the tiny fishes that eat away dead skin cells. One of the few (if not the only) fake treatments shown is the bee sting to the lips to plump them up, although lip plumpers really do contain (usually botanical or chemical, not insectoid) irritants.
According to Julia Roberts, Mirror Mirror is the first film that made her young children aware that their mother was a famous film actress. Even though her children showed a large amount of enthusiasm about the Evil Queen, Roberts did not let them see the film for they were "too young." In fact, Roberts kept her work a secret from her children while Mirror Mirror was filming. "They're too young for it (the movie) and I think they would find it (me) disturbing," she said.
The original script included a scene between a shirtless Prince (Armie Hammer) and the Queen (Julia Roberts) in which the Queen remarks how smooth his chest is. This line had to be altered when Hammer refused to shave the hair off his chest for the scene.
While filming a fight scene between the Evil Queen and Snow White, Julia Roberts accidentally ripped out some hair from Lily Collins.