The Three Mulla-mulgars - Walter De la Mare

Three monkey brothers, Thumb, Thimble, and Nod, are Mulla-mulgars or royal monkeys. As she dies, their mother gives them the enchanted Wonderstone for protection, and tells them to follow their father. They embark on a journey of fantastical adventure to find their father, who left years earlier in search of the kingdom of his brother, the Prince of the Valleys of Tishnar, promising to return for them after he had found the way. (Summary by A. Gramour)