Mix the flour and salt, add the oil and the water and knead the mixture. If too sticky, add a bit more flour.
Refrigerate until needed, covered.
When the works of art have been created with the playdough, bake at 190 C / 375 F / Gas Mark 5 for about 45 minutes to set them.
Notes
If you have powdered paint and want to use that instead, you can add that to the flour and salt instead of adding food colouring to the water.The food colouring is safer though if you don't trust the artists not to eat any of the dough.If you want different colours of playdough, you can also make it in smaller batches and colour it separately.