Two Beavers helped the Pevensie children get to Aslan's Camp and help out in the First Battle of Beruna. In The Lion, the Witch and the Wardrobe, Mr Beaver is presumably the second Narnian that Lucy meets, and the first for Susan and Peter. He gives her the handkerchief that she originally gave to Mr. Tumnus before he was arrested by the chief of police, Maugrim, on behalf of the White Witch.
Mr. and Mrs. Beaver then continued to help the Pevensie children to fulfill the Golden Age Prophecy of when two sons of Adam and two daughters of Eve would bring about the downfall of the White Witch. The children set out on a perilous journey to find Aslan with the help of these two loyal Beavers.
In Prince Caspian, Nikabrik the dwarf claimed that the White Witch had, "Stamped out the Beavers, I daresay; at least there are none of them in Narnia now".