Scrub any rusted areas on the toy with a steel bristled brush. Remove as much rust as possible with the brush.
Sand the toys lightly with medium grit sandpaper to remove any rust that wasn’t removed with the brush.
Put on rubber gloves, goggles and a mask. Spray the cast iron toy with phosphoric acid. Find phosphoric acid at the hardware store. The acid will turn any unseen rust into a crust of iron phosphate. Let the acid work on the toy overnight.
Scrub the toy with a stiff bristled brush to remove the crust of iron phosphate.
Fill a bucket with clean water. Dip the toys into the water to remove any remaining chemicals from the surface. Dry with a towel.
Spray paint the toys with black spray paint for metal. Choose a paint that provides rust prevention. The black paint will serve as a base coat. Hold the paint eight inches from the toy. Spray in a steady back and forth motion, completely coating the toy. Let each coat dry to the touch before applying the next. Apply three to four coats of paint.
Add details and additional colors to the toy with a small artist's brush. Choose acrylic paints that are safe for metal.