This is actually a very hotly debated question. There are some who argue that this poem, with its vivid imagery and exciting plot, is a story that is intended for children and concerns the simple allegorical meaning of the dangers of evil and how it can consume us. Other critics argue that the sexual meaning of the poem points towards a more sophisticated adult audience that is aware of the more sinister meaning in the goblin men and their irresistible fruit. Such critics argue that the poem really concerns the dangers of becoming a fallen woman rather than just dealing with the threat of alluring evil.
Others point to the Christian allegorical nature of the poem to point towards the audience being the Victorian public at large, who need to know the redeeming power of love and how it can reach out and save those who otherwise would perish because of their sin.
What is clear is that this poem is so successful precisely because of the diverse number of meanings that are attached to it. It can be read in so many ways, and can equally be enjoyed by children as well as adults for its multiplicity of meanings.