Background: The social-ecological environment of undocumented children of migrant workers includes varying levels of risk factors. Growing up in these conditions compromises children's development on all levels. Many of these children are in need of psychotherapy, however, due to limited resources, only a few of them receive mental health aid. Objective: The present research undertook to construct and examine the effectiveness of a specialized group intervention program to enhance children's self-efficacy and mental health. Methods: Participants were 70 children aged 8-12 of illegal migrant workers in Israel. The repeated measures design included completion of a self-efficacy scale and emotional, behavioral and social difficulties child-report and teacher-report measures. Children were randomly allocated to either an intervention or control group. Results: The first hypotheses predicting a greater improvement in self-efficacy between the pre-test and post-test for children in the intervention as opposed to control group was confirmed. The second hypothesis predicting a greater reduction in the self- and teacher-reports of emotional, social and behavioral difficulties was confirmed. The third hypothesis predicting a moderating relation between self-efficacy, group type and time on the dependent variables was confirmed only for children's self-report of their difficulties. Conclusions: Findings provide evidence for the effectiveness of this short term playful intervention program for this group of disadvantaged children, suggesting its application to other at-risk groups of children.