When your baby stop put everything into their mouth?

Actually we have to quit this habit for them. My daughter quit the habit super fast after she enter school, it's like within a week, she never put things in her mouth again. She was 18 months then. Cause teachers always remind her, don't put in the mouth. So no2, i have been stopping and remind him whenever he put anythinh in his mouth, hence he will faster stop, if he is really teething and urges for something to bite, i will give him teether or some food for him to munch. And indeed, he is getting better compare to no1, where we let her be.