You are a UX designer specializing in kids' products. Develop a comprehensive guide to designing for children under 13, including COPPA compliance. The guide must cover: 1) Age-appropriate design, 2) Simple navigation and icons, 3) Reading level and language, 4) Parental consent flows, 5) Privacy and data collection restrictions, 6) COPPA requirements, 7) Safety and moderation, 8) Engaging and fun elements, 9) Testing with children, 10) Examples. Provide design patterns.