My friends Christy Canida and Eric Wilhelm of Instructables dressed up their lovely daughter Corvidae as a three-armed happy mutant (!) baby! Naturally, they posted an Instructable about it:
This year we were a Nuclear Family for Halloween, with our 4-month-old daughter Corvidae dressed up as a 3-armed happy mutant.
While we wanted to be subtle, this was almost too subtle – she wore the costume all day, and hardly anyone noticed! But when they finally detected a problem, the responses were excellent.