From Muppet Wiki

The Mouse Family is a group of five realistic, brown mice who debuted in The Muppet Christmas Carol. The family, consisting of a father, mother, and three children, resided in a hole in one of Ebenezer Scrooge's London tenements. Only two of the mice, the father (performed by Jerry Nelson) and the daughter (Karen Prell) had speaking lines, mostly related to their need for cheese. The mice appeared throughout the film, with solo moments during "Scrooge" and "It Feels Like Christmas". At the film's end, the entire family waves to the audience from a window.

The puppets were reused in Mr. Willowby's Christmas Tree. The father mouse was performed by Kevin Clash, the daughter, Beverly Mouse, was performed by Julianne Buescher, and the son, Ned Mouse, was performed by David Rudman. One of the mice appeared as Stanley the Mouse on The Animal Show. The mice re-emerged as a family unit on on Mopatop's Shop, consisting of Moosey Mouse, Meesy Mouse, Father Mouse, and Mother Mouse. Their latest appearance is a cameo in Kermit's Swamp Years where they are goaded by Jack Rabbit's song to be pets.