In school we take care to teach words of civility n emphasise on them using it appropriately; the efforts we take is unless this is practiced by parents at home.
The same goes for avoiding bad language at home n specially in front of kids; even harmless words like, “stupid”, could be easily picked up by a pre schooler. Undo this practice is much more time consuming for us at school but still we do it on a systematic basis.
Often explaining the word helps in the case of an older child.
(For example we tell them a person is stupid when he has no brain n so we should not call anyone with that word as all of us have brains etc. ).
For younger children it is better to ignore it as they generally do it on imitation.
Best examples are us, adults to live a life of how we want them to be; hence it is better to have a check on the words n actions we use in our lives!