The current study constitutes the first attempt to generate repertoires of relational responding, as generalized operant behaviors, when they are found to be absent in young children, using interventions suggested by Relational Frame Theory. Three children, aged between 4 and 6 years, were exposed to a basic problem-solving task that involved two or three identically-sized paper coins in an attempt to test and train patterns of relational responding in accordance with more-than and less-than. On each trial, the experimenter described how the coins compared to one another in terms of their value, and the child was then asked to pick the coin that would “buy as many sweets as possible”. All three participants failed to pass baseline tests for specific patterns of arbitrary more and less responding. Interventions suggested by Relational Frame Theory, including training and testing across stimulus sets, were then successfully used to establish increasingly complex patterns of relational responding in all three children. Generalization tests demonstrated that the relational responding successfully generalized to novel stimuli and to a novel experimenter. In addition, the use of a non-contingent reinforcement condition for one participant, during which no improvement was made, together with contingency reversals for all children, indicated that the trained and tested relational responding may be considered a form of generalized operant behavior. These findings lend positive support to Relational Frame Theory’s approach to derived relational responding, and to the functional analysis of human language and cognition. Alternative interpretations of the data are also considered.