For a younger child, we have to show through example. While eating demonstrate to them-say oh a raisin-I don’t care for them but I don’t want to be rude so I will remove it with either a fork if you are eating with a fork or with the hand if by hand -and do so while covering your mouth and the place it discretely on the plate. You can also once saying you need to remove it excuse yourself to the bathroom and show this as an example For Older children, the same process but once they get the concept to keep them continuing the practice you can add it to a good table manners chart and make it a game to see how many points they can win and determine a reward for that. Older children reading the chart will also be reminded and can see if this is an area they need to improve in which will help with adoption and self-correction ??