Visible crew/equipment: When the baby in the baby stroller is rolling down the cliff hills, a safety wire attached to it is briefly visible, as Luke chases after it.
Visible crew/equipment: The scene where Luke is changing into a mouse, you can see the masking tape on the floor where Anjelica Huston's feet are supposed to be positioned.
Visible crew/equipment: When the witch throws the toy airplane back up to Luke, who is standing in the treehouse, a wire is visible attached to the airplane, guiding it up to him.
Answer: She probably didn't know about her master plan, just about turning kids into mice. Most likely she thought they'd be kept in locked cages and held prisoners.
During the meeting, Miss Ernst says that every child in England must be "Rubbed out. Destroyed." A clear indication that she was talking about killing the children after they get turned into mice but, Miss Irvine doesn't seem shocked or upset after hearing this.