Exposure to influencer marketing of foods and beverages high in fat, sugar, and/or salt (HFSS) increases children’s immediate intake. This study qualitatively explored children’s understanding of, and attitudes towards, this marketing, to elucidate potential mechanisms through which exposure affects behavior. In six focus groups (n = 4) children (10−11 years) were shown a YouTube video featuring influencer marketing of an HFSS product. Inductive thematic analysis identified six themes from children’s discussions of this marketing: (1) YouTubers fill a gap in children’s lives, (2) the accessibility of YouTubers increases children’s understanding of their actions, (3) influencer marketing impacts all—the influencer, the brand, and the viewer, (4) attitudes towards influencer marketing are most affected by a YouTuber’s familiarity, (5) YouTuber influencer marketing is effective because they are not ‘strangers’, (6) children feel able to resist influencer marketing of HFSS products. Children had an understanding of the persuasive intent of this marketing, and although most were sceptical, familiar YouTubers elicited particularly sympathetic attitudes. Children felt affected by influencer marketing of HFSS products, but believed they were able to resist it. Beyond theoretical insight, this study adds to the growing body of evidence to suggest children’s exposure to HFSS influencer marketing should be reduced.