Age Guide: all ages
NASA has some amazing resources for kids of all ages. One easy way to engage with their offerings is to check out their range of podcasts. Whatever the age of your children, there is a podcast with something for them to engage with, great for listening to together and pulling up some great images from NASA's photograph of the day collection.
Try NASA's Curious Universe where astronauts, scientists and engineers chat about a different topic each week or Space to Ground, which has a wrap up of happenings from the International Space Station. Make sure you don't skip What's Up? which is a monthly videocast giving you tips on what to find in the night sky.