What can happen when children do not learn to floss.
The reason why flossing is important is that it helps to remove plaque lodged between the teeth. As plaque hardens it turns into tartar which can only be removed by a oral hygienist or dentist.
Tartar harbors bacteria which produces acids which can damage your gums and cause swelling and bleeding. This is a condition known as gingivitis. Gingivitis if left untreated can lead to periodontal disease which eventually causes bone deterioration and tooth loss.