The purpose of this research is to examine how the moderating effects of health knowledge (inactive vs. active) and advertising’s entertainment level (high vs. low) affect children’s response to advertising’s food content (unhealthy vs. healthy). First, a primary study using the qualitative method was conducted with the purpose of identifying healthy and unhealthy food options based on culture, eating habits, nutritional value and the access of Iranian children to each option so that they could be displayed in TV advertising, advergames and questionnaires. Then, a 2 × 2 × 2 full-factorial, randomized, mixed-effects experimental design was used to test the research framework. 330 students (aged 6–11) participated in the study. The findings revealed that children tended to choose more unhealthy foods after exposure to unhealthy food advertising. This effect was greater for a higher level of entertainment, and was successfully moderated by the activation of health knowledge. It was concluded that embedding health messages in advertising (included TV advertising and advergames) help retrieving children’s health knowledge and therefore, choosing less unhealthy food by them.