This is one of the standard ‘scripts’ that I use with children when we’re working on behavior/rules/procedures.
*sigh* One of the dreadful realities of the preschool world is that children chew on their fingers, suck on their clothing, and yes – eat their boogers. One of our most important goals is to help them learn what is alright to put in their mouths. But keep in mind that they will not master this after hearing it once, or ten times, or a thousand times. It is helping them to break bad habits, and it will take a long time. Be patient, be kind, and wash your hands all the time.
We often talk about how only two things go in your mouth – food and toothbrushes. (Of course they have to say “What about juice?” “That’s a kind of food.” “Well, what about toothpaste?” “That’s something that goes on your toothbrush.” “Well, what about milk?” “That’s like juice – it’s a food.” I really ought to tune up our little saying, but it works for me.)
Anyway, the long and short of it is: when we see a child putting something in their mouth, we say, “That’s not food.” and then ask for the appropriate alternative – please take your sleeve out of your mouth/ please get a tissue/ please go wash your hands.