I stayed in Iceland for 7 days. It was cloudy for the first 5 days, and I almost gave up! On the 6th day, I joined a "Northern Lights Tour". At 2 AM, the guide suddenly stopped the car and said, "Look at the sky!" - Green auroras were dancing overhead, and rare purple light bands appeared! My suggestion: if visiting in winter, stay a few extra days and choose tours with an "Aurora Guarantee" (free re-join if not seen).
I was initially worried traveling with a child would be tiring, but Iceland's family facilities are excellent! The Blue Lagoon has a dedicated "Children's Pool" (38°C water temperature, shallow area), and the "Secret Lagoon" on the Golden Circle has a slide - our child didn't want to leave. We chose apartments with kitchens for accommodation, making it easy to prepare baby food. Tip: Bring waterproof jackets and anti-slip shoes for kids - the south coast is windy and prone to splashing.
Jökulsárlón Glacier Lagoon is the most photogenic place I've ever seen! Best shooting times are 1 hour after sunrise (6-7 AM) and 1 hour before sunset (9-10 PM in summer) when the light is soft, and icebergs appear light blue. Equipment recommendations: Wide-angle lens (16-35mm), tripod (essential for slow shutter water shots), spare batteries (fast drain in low temperatures). Also, the black sand at Diamond Beach easily sticks to lenses - remember to bring a lens cloth.