Maybe starting a geocache series for kids could be fun. Regular size conatiner (or bigger), kid friendly swag, D1/T2 max (or whatever you may find suitable) and no hides above 3 feet (within the reach so the kids can retrieve it alone) could be fine. That way other parents could contribute and participate in the process of teaching navigation to children. In our region a thing like this was done for a bicycle tour. It worked pretty well.
There are portable sundials. They fit into a shirt pocket and can be adjusted to your latitude. I own a brass one with a diameter of about 2 1/2". They show the time and north at the same time (teaching different ideas of "north" can be done here). That can help to get a concept of telling the time by the position of the sun. Later it may help to teach about the seasons and even start on celestial navigation. Celestial navigation would be strictly optional and beyond their comprehension now. The sundial is also available as a carton model set ( sundial ). Building it and using it may be some fun. I own that one too. It´s pretty accurate but the kids will need some supervision and maybe help for building it. The series has some other educational items to build from carton. They really work and building them helps to understand how they work.