Children learn to regulate themselves independently at preschool age; thus, adjustment is necessary to improve. Several studies have found the relationship between cool executive function and the development of adjustment. However, little is known about the impact of cool executive function intervention to enhance the adjustment of preschool children. This study investigated the efficacy of an online intervention that focuses on cool executive function components (inhibitory control, working memory, and cognitive flexibility) in improving children's adjustment during COVID-19 pandemic. The study included seven sessions consisting of 4 different tasks (self-ordered pointing task, flanker task, stop-signal task, and flexible item selection task), which lasted approximately one month. Sixty-four children (48-72 months) who participated in the study were randomized into an experimental or control group. Pre- and post-assessments conducted using Child Adjustment and Parenting Self-efficacy (CAPES). Changes in children's adjustment were analyzed using the analysis of covariance (ANCOVA). The results indicate that the adjustment among participants has improved significantly only in children aged four years (48-59 months). This finding suggests that the cool executive function intervention can promote early child adjustment by adding another aspect of EF, even in a pandemic condition.