If you use oil pastels, they’re going to get dirty as heck.
You’ll get colors all over each other and unlike with paints you do not need anything special to clean up.
All you need to do is grab a paper towel, tear it up into little squares, hold a square in one hand, the pastel in the other, and spin the towel around the pastel till clean. Fold the square over and over to get a new clean surface.
You’ll have your oil pastels ready for a new painting in a bit.