Here is an idea using those clear wishing stones you find in all good cheap shops.
Turn them over and paint the flat side.
(When you turn them right side up, the image you paint will be magnified)
This is a little tricky.
We kind of have to paint ‘backwards’
First thing that you paint will become the ‘topmost’ layer of your artwork.
So, to paint a butterfly with blue spots, paint the yellow outline of the butterfly, AND the blue spots too.
Then, you add the filler colours, and the background colours too.
When the acrylic paint is completely dry, you can turn them over and attach a small circle of sheet magnet. You can often buy it with a sticky back, so it is as simple as peeling off the protective layer and fixing in the right spot. If not, use a really strong glue. (not craft glue).
They would make a pretty cute addition to the fridge or your funky noticeboard, wouldn’t they?
Personalise them in your favourite colours, or make up a set for a friend in her favourites?
(You might also try it with a pretty sheet of origami paper cut to size, or vinyl stickers?)