I thought altering Hot Wheels would make a great 1-hour project for our maker club, which includes preschoolers all the way to upper elementary kids. They were given a lot of choices for their mod-terials, things like magnets, metal and paper scraps, beads, glitter and paint markers. Some of them made their cars anthropomorphic, some engaged in an arms race, and some of them were just excited I let them use glitter today!
I did some prep a full 24 hours in advance, spray painting their cars.
I taped the wheels and windshields with washi tape, although I think masking or gaffers tape would also work well. Then I sprayed them a rainbow of colors and let them dry overnight- dry time is key- they were tacky for hours after. I used two or three coats of paint depending on the car. I think the spray paint and paint markers will not have the longevity that stripping the paint and using modeling paint might have, but it worked well enough for our purposes and avoided harmful chemicals (mostly).
This one is mine- cat creature and lizard buddy just got married! They even have little soda cans tied to the back of the car.