Make a Family Film!
Kids know tech - and making a family movie is a great way to let them show this off, while getting some amazing moments on film. Let them decide on the approach - something scripted, fly on the wall, or maybe even stopframe. Then work on it together, letting them call the shots. When the filming's done, there are plenty of free editing packages out there. If it's something you've not done before, you could all pick up a new skill.