Copenhagen is a very walkable city and has so many great photo opportunities. Wear comfortable shoes and be sure cell phones and cameras are fully charged before leaving lodgings. It helped us tremendously to pack portable cell phone chargers.
Most of Copenhagen's attractions and museums have cafes, restaurants and resting areas. Keep in mind of Copenhagen's fast bicycle traffic. Always be aware of the busy city's cyclists, so be careful with little kids.
The Nationalmuseet and Ny Carlsberg Glyptotek/The Glyptoteket are closed on Mondays and weekends are high-volume days. Ny Carlsberg Glyptotek/The Glyptoteket is free for everyone on Tuesdays.
The Nationalmuseet and Ny Carlsberg Glyptotek/The Glyptoteket are free for kids under 17 years. The Ruins under Christiansborg Palace are also free for children. The Copenhagen Card allows free admission into 79 museums and attractions. Plus free transport by train, bus, harbor bus and the Metro in the entire Copenhagen Region and also to/from the airport in Zones 1-99. It is a huge money saver.