'Use your imagination' is a statement often associated with adolescents and adults, not with children. With them we say with admiration, 'what an imagination you have.' In the statement, there is a longing as one is separate from the experience.
From a child's perspective, they know nothing of the meaning, no sense of absence. How are they to conceive what they are? Because a child isn't separate from the experience of imagination. For instance, while playing they look happy, which is their state and experience.
Unlike the adult; forever striving, searching, pondering and hoping for a rekindled imagination and happiness. Why such effort for consistent happiness? It appears the death of imagination is the death of happiness in its purest form.