Build a solar system you can look up at
Most space toys sit on a shelf. This one hangs. Children assemble the frame, paint the planets and then fix each one in its place, so the order of the solar system becomes something they have physically put together rather than memorised from a page. The finished mobile measures 75 cm x 75 cm, so it needs a clear patch of ceiling or a spot well out of the way of ceiling fans, doors and tall bookshelves. At that size each planet has room to be seen on its own, which makes the differences between the gas giants and the small rocky planets easy to point out.
Making that holds an 8 to 12 year old's attention
At this age, a multi-step project with a visible result is what children are ready for. Following the instructions in sequence builds planning and patience. Painting small pieces steadies the hand and asks for the same careful control needed for neat handwriting and detailed drawing. The project grows with them: at 8 they follow the steps with an adult nearby, and by 11 or 12 they plan their own colour choices, work through the build alone and teach the planet order to everyone else in the house. The bonus wall chart gives them facts to read as they work, which keeps the build connected to the science. Older children start quizzing the family on planet order before the last piece goes on.
After the build: glow and display
Once the lights go off, the planets glow in the dark. The glow comes from the planets themselves, so there are no batteries to replace. Glow-in-the-dark finishes need light to charge, so hang the mobile where it catches daylight or room light. Expect the glow to be soft rather than bright, so it works as a night-time feature and not a night light. Because the project is calm, quiet and self-contained, it suits a wet weekend or a school holiday afternoon. It can be done solo at the table, or as a shared build where an adult helps hold pieces steady while the child makes the decisions.