I had this bright idea. Shaving cream, food colouring, toddler .....
I thought it might teach him some interesting concepts about what happens when two colours get mixed, and a nice sensory experience with touching different textures.
The reality: 2 minutes preparation, 5 minutes 'play' (mostly tantrums), 45 minutes clean-up including bath and hair-washing.
Lessons learned: next time, child STARTS activity naked.