The child doesn’t understand the negative concept as stated in the words “do not”. The child understands a positive instruction followed, perhaps, by gentle assistance in achieving the desired outcome. So too is this true about the person who litters, I’ve found.
“Don’t litter” is an ineffective message. At the Litter Prevention Program we believe that positive sells. We encourage people to do something good like respect the environment, use the proper bins, ‘think, look, place’, be clean – strong words that are far more easy to embrace than any negative, bordering on hostile, messages against littering like 'No. Don't'.
Consider the word ‘anti’ as in anti-litter campaigns. Anti means against. It rails in opposition and is not typically positive or proactive. With litter prevention we want to do more than oppose it, we want it stopped.
With the right approach and ingredients littering can be stopped. As with a young child, saying “don’t” to someone who litters isn’t the wisest approach.