This dataset supports the project “Domain-Generality Is an Emergent, Not Inherent, Property of Metacognition” and contains adult and child data from episodic memory and perceptual tasks designed to study confidence judgments across domains. It includes preregistrations for two experiments, stimuli and experiment programs in MATLAB or PsychoPy, experimenter materials for children, raw and analysis-ready data files labeled “Absolute” (Experiment 1) and “Relative” (Experiment 2), separate memory and area task spreadsheets, wide-format files for JASP or SPSS, and analysis code and outputs in R markdown or JASP. The dataset is intended to examine confidence bias, sensitivity, efficiency, and developmental changes in cross-domain metacognitive processing.