The originality of the setting in which therapeutic mediation techniques, for example, painting, pottery, modelling, are employed in child psychosis rests in the fact that the child can thus engage with an attempt at representation based on sensory modalities. These include the child’s own sensorimotor aspects and the sensorial qualities of the “malleable medium”. The manner in which he or she makes use of this is part of the transference dynamics. The clinician must therefore extend his or her capacity for attentiveness in order to take into account these various forms of sensorimotor expression. In child psychosis and autism, it is essential to focus on the kind of associativity that is an integral feature of body language and behaviour. In this paper, the author describes the specific nature of symbolization processes and of transference dynamics in mediation-based therapies, with particular emphasis on the importance of the transference onto the malleable medium and of the transference that makes use of sensory diffraction.