Crayola manufactures several products designed specifically for window decorating including: Crayola Window Markers and Window Crayons. If you're unable to locate either of these products, Take Note! Dry Erase Markers or Crayola Washable Paint can be a fun alternative.
Pro Tips for Washable Paint:
For the perfect mixture, add equal parts Crayola Washable Paint and dish soap.
Add a pinch of flour to make the paint thicker.
Don't forget to protect the area under your window by laying down an old T-shirt.
Painting can be done on the inside or the outside of your window.
Because soap is used in the paint, your designs will wipe off windows with a wet paper towel. You can follow up with window cleaner for extra shine.