Which word describes causing mischief and being playfully naughty?

The term that best captures the essence of causing mischief and being playfully naughty is "mischievous." This word conveys a sense of playful teasing or light-hearted troublemaking, often associated with innocent fun rather than harmful intent. It encapsulates behaviors that are spirited or cheeky, typically in a way that might provoke a smile or laughter rather than serious concern.

In contrast, the other words do not share this playful connotation. "Serious" implies gravity or solemnity, which is the opposite of a light-hearted or mischievous attitude. "Cautious" refers to being careful and avoiding risks, which also contradicts the idea of playful naughtiness. "Disinterested" describes a lack of interest or concern, further distancing itself from any playful or mischievous actions. Therefore, "mischievous" is the word that accurately fits the description of being playfully naughty.