Two studies examined the role of swimming competence on children's motivation and intentions under the framework of the integrated model of self-determination theory (SDT) and the theory of planned behavior (TPB). The studies were conducted to investigate the direct and moderating effects of swimming competence on the psychological pathways and constructs in the model integrating SDT and the TPB. Study 1 utilized a cross-sectional survey involving 4,959 primary school children, and examined the relationships between swimming competence and the model variables. Study 2 employed a pre-post-test quasi-experimental design with 1,609 primary school children to assess changes in swimming competence and its association with shifts in the model variables. In Study 1, significant positive relationships were found between swimming competence and all model variables (β = .061 to .330, p < .05), except for intention (β = -.009, p > .05). The moderation effects of swimming competence on model parameters were either small or not statistically significant. In Study 2, improvements in swimming competence correlated with change scores in all model variables (β = .046 to .230, p < .05), except for subjective norm (β = .049, p > .05). Notably, swimming competence did not significantly moderate the parameter estimates of the integrated model at the change-score level (p > .05). Our two large-scale studies demonstrate that the psychological pathways of the integrated model of SDT and TPB are robust across varying levels of swimming competence. The findings suggest that sports training programs for children should not solely emphasize competence development or skill acquisition. Instead, they must also consider the motivational and social cognitive factors that influence children's long-term intentions to engage in a sport. Enhancing these psychological aspects may be essential for fostering sustained participation in physical activities like swimming.