This device is a centripetal force demonstration toy designed in OpenSCAD, fully parametrically, so it can be modified to fit your needs. Great for students new to physics!
Here is a link to the wikipedia page for centripetal motion: https://en.wikipedia.org/wiki/Circular_motion
When rotated quickly, the two balls inside the device move away from each other due to centrifugal force. The faster one spins the toy, the farther up the balls go.
The main equation to teach here is F=(mv^2)/r, that is, the force that pushes the balls outward is equal to their mass times their velocity squared, all over the radius of the curve!
Even if the kids are not old enough to learn the math behind it, this is still a good toy with which to introduce the concepts.
In total, this toy took about 50g of filament to make, meaning the cost equates to about $1.33 per toy! Compare this to similar existing toys on he market that cost around 10 dollars a piece. https://www.scientificsonline.com/product/spill-not
Other existing options come in expensive physics kits. This is much cheaper!
See the toy in motion here: https://youtu.be/iUkh8BlpaQw