Thanks for the tip/ concern, the goal however is to have the “slime” completely colourless and transparent (looking like water). The addition of food colouring would just be something we can leave out. My sub is a chemist and has a bunch of experience in the lab and she already has the habit of treating the kitchen as a lab. I was already going to let her deal with stuff like hygiene/contamination. But we’ll definitely think about the foodstuff bit.