The inner child is not a metaphor — or rather, it is a metaphor that points at something real. Every adult human being carries within them psychological structures formed in childhood: patterns of relating, core beliefs about safety and worth, emotional responses that were adaptive then but may be limiting now, and the accumulated residue of both wounds and gifts from the first years of life. "Inner child work" is the term for the practice of consciously engaging with these structures — of meeting the younger self who formed them, understanding their logic, and healing what needs healing.
The concept has roots in psychoanalysis — Freud's understanding that early experiences shape adult personality, Jung's conception of the Divine Child as an archetype of wholeness and potential — but its modern form was developed primarily by John Bradshaw, whose books and television series in the 1980s brought inner child work to mass audiences. Bradshaw drew on Eric Berne's transactional analysis (which distinguished Child, Parent, and Adult ego states as active in adult psychology), Alice Miller's devastating critique of how childhood emotional needs are systematically disregarded by parents and institutions, and humanistic psychology's emphasis on the healing power of unconditional positive regard.
The clinical reality that inner child work addresses is straightforward: childhood experiences — particularly experiences of neglect, criticism, emotional unavailability, abuse, or overwhelming stress — leave traces in the nervous system and the personality that persist into adulthood. The child who learned that expressing needs led to rejection develops an adult who cannot ask for help. The child who was shamed for their emotions develops an adult who cannot feel them. The child who was praised only for achievement develops an adult who cannot rest. These patterns are not character flaws; they are adaptations that made sense given the child's situation and that have never been updated to reflect the adult's greater resources and different environment.