Introduction: Childhood obesity is associated with impaired health during childhood and it is a risk factor for later adult diseases if left untreated. There is a rising trend of over nutrition in developing countries including India. Hence the present study has been envisaged to determine the modifiable risk factors of overweight/obesity among 5-18 years old children of a tertiary care centre in South Kerala. The objective of this study was to identify the modifiable risk factors related to obesity among the study subjects. Methods: After getting ethical committee clearance this cross-sectional study was conducted among children between 5 and 18 years of age in the department of paediatrics of a tertiary care centre in South Kerala, during the period between August 2018-October 2020. The BMI was plotted and analysed with appropriate software. Modifiable risk factors for obesity were elicited using a semi-structured questionnaire with questions included from WHO STEPS instrument. Results: Among the 250 children the proportion of obesity and overweight was 88 (35.2%) by IAP standards, 63 (25.2%) by WHO standards. According to this study among the over nourished children 62 (70.5%) had at least one meal per week, which was not cooked at home. There was a significant association between hotel food intake and over nutrition. Children taking hotel food (p value < 0.001) were more obese than those not taking hotel food. Those children who watched television while having food had a greater chance of becoming over nourished. Majority of over nourished children consumed snacks on a daily basis. Physical activity like cycling and vigorous intensity sports were also found to be less in overweight/obese. Conclusions: Our data showed a high prevalence of unhealthy eating behaviours reported by the participants. Epidemiological data provided by this study suggests the urgent need to design preventive interventions. Childhood obesity problem can be reduced by educating children and parents about healthy nutrition and encouraging them to be physically active.