Despite the health benefits of physical activity (PA), many individuals do not meet PA recommendations. Family-centered PA approaches, particularly active engagement by Mexican-heritage fathers, may support family PA. This study reports PA outcomes of a culturally tailored, father-focused, and family-centered, program for Mexican-heritage families. Promotora researchers recruited participating families (n = 59, n = 42 complete cases), consisting of children (mean age: 10.1 [SD = 0.9]), fathers, and mothers from five randomly selected geographic clusters in low-resourced colonias in south Texas, in a stepped-wedge randomized design. PA was measured using wrist-worn ActiGraph GT9X accelerometers. Statistical analyses for moderate-to-vigorous PA (MVPA), light PA (LPA), and sedentary time for the child, father, and mother were conducted using linear mixed models. The findings were as follows: children had no significant changes in MVPA (p = 0.18), LPA (p = 0.52), or sedentary behavior (p = 0.74); fathers had no significant changes in MVPA (p = 0.94), LPA (p = 0.17), or sedentary behavior (p = 0.15); and mothers had a significant decrease in LPA (p < 0.01), and no significant changes in MVPA (p = 0.66) or sedentary behavior (p = 0.77). Despite null results, this study provides an example of a culturally tailored, family-focused program implemented among Mexican-heritage families with limited PA resources and opportunities. Future PA interventions may require higher PA-focused doses over longer time periods to produce a significant change in LPA, MVPA, or sedentary time.