Despite the critical importance of attention for children's self-regulation and mental health, there are few task-based measures of this construct appropriate for use across a wide childhood age range including very young children. Three versions of a combined go/no-go and continuous performance task (GNG/CPT) were created with varying length and timing parameters to maximize their appropriateness for age groups spanning early to middle childhood. As part of the baseline assessment of a clinical trial, 452 children aged 3-12 years (50% male, 50% female; 52% White, non-Hispanic, 27% Black, 16% Hispanic/Latinx; 6% other ethnicity/race) completed the task. Confirmatory factor analysis indicated that all task versions assessed two latent factors, labeled response inhibition and sustained attention. Versions for older children elicited lower overall accuracy while equating levels of inhibitory demand. All versions showed limited floor and ceiling effects, as well as developmental sensitivity. Boys showed higher commission error rates and children from lower income households showed lower performance across multiple task metrics. Task metrics, especially d prime and accuracy summary scores, correlated with parent-reported executive function and externalizing behavior. Task scores show promise as valid and sensitive indicators of inhibition and sustained attention across heterogeneous pediatric age groups. (PsycInfo Database Record (c) 2023 APA, all rights reserved).