(1) Background: Childhood obesity is a public health problem. The purpose of this study was to know if exposure to commercial messages which advertise food products exerts any effect on the short-term consumption preferences of 4- to 6-year-old children. (2) Methods: A double-blind and randomized experimental design. Sample consisted of 421 boys and girls from twelve schools in a city in Spain. (3) Results: In three of the four product pairs shown, the products advertised in the intervention were preferred. In the results of applying the model for the first product pair presented, sugared cereals, the predictive variable which best explains the behavior of the preferences expressed is gender (Odds Ratio 0.285 (0.19–0.42); p < 0.05). For the second pair, chocolate cookies, the family’s nationality has a strong weight in the model. As regards the regression model calculated for the last pair (filled rolls), the predictive variable which showed having more influence was gender. Boys had a 1.39 times higher risk of selecting the advertised product than girls. (4) Conclusions: The persuasive effect of commercials has shown to be influential in a general, immediate, and significant way only in the case of products with wide brand awareness. This study reinforces the importance of advertising and emphasizes the need to initiate measures to control the content of TV commercials.