This activity is not suitable for children, since magnets can be swallowed and could cause life-threatening complications.
But kids can help with "baking" and painting the cakes.
The glueing should be done by adults.
Holding the magnets
In order for the magnets to stay on well, you should apply pressure for about 20 seconds.
Decorating the cakes
Finally, you can decorate the painted plaster cakes with pearls and other deco elements.
You can use normal PVAC glue, which becomes transparent when dry.