Chronic non-communicable diseases (CNCD) show an increasing tendency, especially in low- and medium-income countries. It is necessary to develop and evaluate strategies to strengthen healthy habits at an early age in these countries. Objective: To determine the effect of the health promotion strategy “United for Healthier Kids” (U4HK) on health lifestyle habits of a group of Colombian schoolchildren for the 2018-2020 period. Materials and methods: This quasi-experimental study features treatment and control groups and pre- and post-intervention measurements. The study involved 1,011 schoolchildren between six and twelve years old from seven rural and urban schools of the Sabana Centro region of Colombia. We used the Healthy Habits Measurement Tool, previously validated in Colombia. Results: When comparing within and between groups, the UHK strategy showed statistically significant differences in healthy habits (p < 0.05) related to nutrition and physical activity in schoolchildren. Conclusions: The U4HK strategy had a positive effect and impact on the schoolchildren’ healthy habits, especially in the ‘chooses to drink water’ and ‘moves more’ components. There were statistically significant differences (p < 0.05) between groups in four out of the five categories: drinks more water, chooses nutritios and varied options, eats and cooks as a family, and moves more. The U4HK strategy responds to current and future health problems in schoolchildren and helps prevent chronic diseases. It could be replicated in similar populations.