Appearance of an unknown child in a dream can signify various underlying themes and emotions, often pertaining to aspects of the dreamer's inner self or life experiences.

1. New Beginnings: An unknown child can symbolize the emergence of new opportunities or phases in the dreamer's life. This could include new projects, relationships, or personal growth.

2. Untapped Potential: The child may represent potential that the dreamer has not yet realized or acted upon. It could indicate talents, ideas, or aspirations that are neglected or still developing.

3. Innocence and Vulnerability: An unknown child might reflect the dreamer's own feelings of vulnerability or innocence. It can also highlight a desire to return to a simpler, more carefree time.

4. Responsibility and Nurturing: This dream may suggest a need to focus on nurturing and caring for some aspect of one's life or self, whether it be responsibilities, relationships, or personal development.

5. Unknown Aspects of the Self: The appearance of an unknown child can indicate unexplored or subconscious parts of the dreamer's psyche that are seeking attention or integration.

6. Anxiety Over Uncertainty: The presence of an unfamiliar child might evoke feelings of unease or anxiety about uncertain or unfamiliar situations or responsibilities in waking life.

7. Loss or Longing: For some, the dream might touch upon feelings of loss or longing, perhaps for childhood, simplicity, or a phase in life that has passed.

8. Symbol of Creativity: Often, children in dreams are symbols of creativity and the birth of new ideas. An unknown child might suggest that the dreamer is on the cusp of a creative breakthrough.

Interpreting the appearance of an unknown child in a dream can vary significantly depending on the dreamer's life context and emotional state. It is important to consider the specific emotions and situations within the dream for a more personalized understanding.