Sounds great, I've never tried a window aimed specifically at play, just cleaned mud, handprints, smiley faces & bird visits from the house ones
agree with avoiding acrylic paint - finger paint that uses a gel base may apply well to smooth surface & give a transparent appearance .. would there be time to cook up a plain cornflour - or arrowroot - & water mix & add paint to it ?
Interested to hear if anyone has tried Vege-Gel as a finger paint !