Objective: Individuals with ADHD have deficits in reward processing and related cognitive tasks such as delay discounting and risky decision-making. The ventromedial prefrontal cortex (vmPFC) and dorsolateral prefrontal cortex (dlPFC) are two distinct cortical areas that are involved in reward processing. Methods: Twenty children with ADHD received transcranial direct current stimulation (tDCS) in three separate sessions with one of three montages each, including anodal/cathodal tDCS over the left dlPFC and right vmPFC respectively, the reversed montage, and a sham stimulation condition. During stimulation, in each session, participants performed the balloon analogue risk taking and chocolate delay discounting tasks. Results: A significant effect of stimulation condition on emotional processing was observed. Specifically, anodal tDCS over the right vmPFC, coupled with cathodal tDCS over the left dlPFC, reduced risky decision-making and delay discounting. Conclusion: These results imply that the left dlPFC and right vmPFC are involved in reward processing in children with ADHD. This finding is discussed in the light of the delay aversion theory of ADHD.