This article explores the question of the instrumentality of children's comprehension and interpretation of metaphor and nonsense for the development of imagination and creativity. It provides a theoretical foundation and experimental data relevant to the investigation of the inner mechanisms of imagination. The author argues that imagination is an aspect of sign-symbol activity and one of the conditions for creativity development. From this point of view, metaphorisation and nonsense interpretation are sense-oriented substitutions. Original experimental data (measurement of unknown object's attributes by known characteristics, metaphor's "animation" and independent structuring, attribution and interpretation of nonsense, etc.) demonstrate that stimulation of the construction of new contexts (frames) helps to build new ontogeny fragments and create new senses.