The aim of the present study is to evaluate the preliminary efficacy of a family intervention with third-wave therapy strategies to promote parental psychological flexibility. Seven mothers aged 31-50 years participated. To assess the effects of the intervention, parental psychological flexibility, avoidance, emotional regulation, parental stress, and satisfaction with life instruments were used at the end of the intervention and at 3 months follow-up. Mood and coping were assessed as the process measure. The effects on their children were assessed with the scale of strengths and difficulties. Intervention comprised four two-hour sessions. Results showed positive effects in the psychological flexibility and emotion regulation of mothers. In children, there was a reduction in emotional symptoms and hyperactivity. This study provides preliminary evidence of the efficacy of third-wave based family interventions.