As kids encounter food advertisements, it is important that they be able to critically evaluate the message's claims, the healthiness of the promoted product and their desire for it. To explore how technology might help kids develop these skills, we created an online forum called TalkBack that encourages children to critically analyze the messaging in food ads and their attitudes towards marketed foods. We evaluated TalkBack with twenty-eight middle school students in a summer camp program. We discuss how participants appeared to project and protect their sense of self through their interaction with TalkBack. We also describe the limited analytic depth of their forum contributions and suggest directions for HCI research that attempts to encourage critical thinking and health promotion in adolescents.