Short-form video has become the primary way parents discover, compare, and evaluate preschool-education brands. Managers still lack clear guidance on how often to post and how long videos should be, and whether these choices should differ between TikTok and YouTube (Shorts and skippable In-stream). This study proposes a complete, platform-level research design that combines a multi-arm field experiment with a staggered-adoption quasi-experiment. We test four controllable levers: posting cadence, video length, creative richness (expertise, authenticity, heritage cues), and call-to-action (CTA) placement, on lower-funnel outcomes: click-through to trial pages, lead submissions, and paid sign-ups. We measure attention using viewing time and completion thresholds, which are well-established indicators of advertising impact. To identify causal effects, we combine randomized exposure in a field experiment with modern Difference-in-Differences and event-study approaches that leverage natural shifts in content scheduling. The study is designed to pinpoint each platform’s “sweet spot” for video cadence and length, clarify how attention shapes downstream outcomes, and translate these insights into an actionable playbook for preschool-education marketers. Our approach builds on emerging evidence about vertical mobile video, skippable formats, creator influence, and short-form content dynamics, bringing these strands together in a unified framework.