What is night night vs goodnight?

"Night night" and "goodnight" are basically the same thing. Both are used as expressions of farewell, intended to wish someone a peaceful and restful sleep. "Goodnight" is the more common phrase used in the English language, while "night night" is more commonly used with children or in a more playful context. "Night night" can also be seen as a variant or a more informal way of saying "goodnight." Ultimately, the choice between the two will depend on the speaker's personal preference and the situation in which it is being used.