"The weasels and the mice run in the house."
Translation:Mustelae et mures in villa currunt.
-que is just another way of saying "and."
It attaches at the end of the 'second member' of the group: puerī et puellae, OR puerī puellaeque.
(It can 'attach' other parts of speech as well, not just nouns.)
ADDENDUM: "with mice" is the prepositional phrase cum mūribus .