Sedentary lifestyles and unhealthy diet are the main reasons of childhood obesity. This paper presents MyHealthyKids: Intelligent Web-mobile Children Obesity Intervention System for Primary School to manage and reduce the problems. The main objective of the system is to prevent and to reduce childhood obesity cases that are currently increasing in primary schools in Malaysia. MyHealthyKids consists of three main modules: obesity prediction, children persuasive and recipe suggestion module. The Naïve Bayes is used to predict whether the children are prone to be obese; the persuasive technology is used to encourage the children to participate in physical activities and change their eating habits; and the knowledge-based system is used to suggest a suitable menu for canteen operators in order for them to prepare healthy food for school children. Preliminary test has shown that the system has 73.3% accuracy for prediction and gets good feedback from the children