To discover the reasons behind invited families' lack of engagement with a family-based childhood obesity programme in a deprived area. Interviews were conducted with 10 families who were invited to join the programme, but declined to engage. There were two distinct subgroups of participants: those who had no interest in attending the programme and those who showed initial interest yet did not continue attending. The two subgroups were analyzed separately using inductive thematic analysis, and then compared. Analysis identified eight themes overall. For both groups, when the service was perceived to be not needed ('I didn't see how that would help'), the families disengaged with it. For both groups, this perception was partly related to the perceived appearance of their children: either that they were not obese ('I didn't think my son was overweight') or that they were growing into their size. There was also a similarity in both groups that they perceived that they were already following healthy lifestyles. In addition, several of the themes arising from the families who had no initial interest were related to the impact of the letter that parents received detailing the result of their child being weighed and measured at school. This angered parents ('I was disgusted'), and there was a feeling that the approach was too generic. This study identified a number of potential reasons behind why families may decline to engage with a childhood obesity programme in a deprived area. Across all families, if the programme was perceived as not needed, they would disengage. For those who did not engage at all, the initial communication of the child's body mass index (BMI) is crucial. Recommendations include taking a more personal and tailored approach for the initial communication and shifting the focus of the programmes onto healthier lifestyles.