Modern Fantasy suspends disbelief and the characters must be believable. The setting is where anything can happen, and the reader must be convinced that the new worlds exist. They should be able to hear and see it.
The themes can be: universal struggles, values, emotions: good vs evil, faith and perseverance, personal and social responsibility, and love and friendship are valued.
(Through the Eyes of a Child: An Introduction to Children's Literature by Donna E. Norton)