Every child experiment withs curses and ugly words. Profanity is often heard on the streets, on television, in our environment. It is a part of language and folklore of every nation, and has its rightful place but the children do not know when it is appropriate to curse and therefore we must try to make children understand that curses are not nice words.
Be ready to have the biggest problem with your surroundings (family, friends ...), who will find it funny and interesting when the children say bad words, and maybe they will encourage or even teach them new bad words. On the other hand, it is very interesting for children to be in the focus of attention while swearing.