Objectives: Limited research exists on how new computer science (CS) teachers understand fundamental Internet principles. This knowledge gap hinders the development of effective upskilling courses, especially as new CS curricula are being introduced worldwide. This study investigates new CS teachers' conceptions of fundamental Internet principles, compares them with children's understanding, and examines the relationship between teachers' Internet knowledge and their knowledge of basic digital trace topics. Study Methods: A convergent mixed-methods approach was used, involving semi-structured interviews and drawing tasks with 50 new CS teachers. Data from a separate sample of 165 children (Grades 4, 6, 8) were included for comparison. A thematic analysis and frequency analysis of interview transcripts were conducted. Findings: Most new CS teachers recognized the Internet as a global network but had varied and often unstable conceptions about data storage and transfer. Compared to children, teachers demonstrated a more advanced understanding but still exhibited substantial knowledge gaps. There was no significant correlation between understanding Internet principles and basic digital trace topics, though a moderate relationship was found regarding news feed personalization. Conclusions: The study highlights the need for targeted interventions to improve new CS teachers' understanding of Internet principles, especially the invisible aspects, such as data storage and transfer mechanisms. By providing new data on a rarely studied group, this study contributes to both CS education and broader fields like developmental psychology and conceptual change, offering insights into the developmental trajectories of Internet comprehension and the integration of everyday and scientific knowledge.