This study of 14 Australian immigrant mothers from Bangladesh, India and Pakistan, and their 12 children aged eight to 11 years, explores the interplay of cultural and social processes which might elevate the risk of obesity. Mothers and their children were asked in semi-structured, face-to-face interviews about changes in their diet and physical activities after immigration to Australia. Thematic analysis of these interviews showed a transformation in immigrant families' diets and physical activities as they transitioned from their traditional lifestyles to an Australian pattern. Both mothers and their children recognised the problem---and causes---of obesity. However, different frames of reference---origin countries for mothers and Australian peers for children---resulted in generational disjuncture about healthy bodyweight and the strategies to achieve it. Mothers' cultural values and low social status in origin countries, led them to struggle to adapt to new health behaviours. In contrast, their children wanted to look and act like their Australian peers, who valued slimness. Our findings reveal that the social status of food and activity reflects cultural meanings from both origin countries and Australia, creating contradictions and tensions for immigrants that public health campaigns will need to help them navigate.