The expression 'quiet as mice' is a puzzling one, because mice can often be very noisy, so people who are being quite as mice may in fact be squeaking and scrambling around. The expression 'quiet as mimes' is more appropriate, because mimes are people who perform theatrical routines without making a sound. Mimes are annoying and embarrassing, but they are much quieter than mice, so 'quiet as mimes' is a more proper way to describe how Violet and Sunny got up from their bunk, tiptoed across the dormitory, and walked out into the night.
