Once upon a time there were lots more stores selling basic electronic parts than seems to be the case these days. One class of such parts is known as "ferrite magnets" They are basically a ceramic that has a high content of magnetic iron oxide, and and at some point during the manufacturing process,
they are permanently magnetized.
Ferrite magnets are not especially strong, but they are quite adequate for this Toy Idea. Note that they are manufactured in different sizes, shapes, and magnetic orientations (relative to their shapes). For this Idea, we need a disk-shape that has a hole in the center (like a very thick and wide washer). One face of the magnet is North, and the opposite face is South.
You need at least six, but probably not more than ten, of these ferrite magnets. A few of them don't weigh much, but too many will make it more difficult for a small child to hold. Next, ferrite magnets are generally a boring grayish color, and upon touching them you will discover that they will easily make your hands dirty, so this aspect needs to be addressed immediately.
Spray them with shellac (which solves the dirtiness problem but doesn't affect their color much), or paint them with a type of paint that dries into a fairly tough plastic coating (which can solve both problems if you use several different paint colors).
After the coating dries, you need a dowel, which is just a little smaller in diameter than the holes in the ferrite disks. Part of the dowel should be wrapped with handgrip material. The rest of the dowel will hold the magnets.
After threading the first magnet onto the dowel and gluing it in place, the second magnet should be threaded such that the two will magnetically repel each other. This second magnet must be free to move (the first is glued to act as a finger-guard). The third is threaded such that it magnetically repels the second. The fourth is threaded such that it magnetically repels the third. And so on. Make sure the dowel is long enough for a reasonable gap (at least half a centimeter) to exist in-between each pair of magnets!
After all the magnets are threaded onto the dowel, a heavy plastic washer can be screwed/attached to the far end of the dowel, to retain the magnets (the last magnet might be glued to it, to reduce noise).
Now hand it to the small child. In holding it by its handle and moving it about, the magnets will bounce along the rest of the dowel in a fascinating way. It will take some serious jerking to make some magnets overcome their mutual repulsion enough to clash together and thus make noise. The rest of the time, this toy is nice and quiet.