Dick King-Smith: Poppet [1999] paperback

Poppet is a little African elephant. When he is born, his mother warns him against mice because they run up elephants' trunks. Poppet spends some time asking various creatures if they are mice and then, to his horror, one of them says 'Yes'. However, Momo the mouse persuades Poppet that he's been told an old wives' tale and the two become friends. Poppet's mother is horrified but is won over in the end by Momo's eloquence.