Ok... tell me if you know the name of a movie with this description in a way... not sure how old it is so... OK two kingdom(not sure) two place at war with each other... but the girl of one and a boy of the other fall in love and you... They want the war to stop so, goes to this witch(person) I think... she tells them to go lay on a tree to forget each other feelings but doesn't work and as to take potion which make them slowly disappear... the two families are blaming each other and at the end they forgive each other just in time so the couple do not disappear and then after reappears... I think there could have been fairies, not sure but they were smaller or the size of a mushrooms,

Are you thinking about The Magical Legend of the Leprechauns with Whoopie Goldberg, Randy Quaid, Colm Meaney, et al?

The Magical Legend of the Leprechauns (1999) (TV) (http://amazon.imdb.com/title/tt0205214/)

Well thank you, yes I think that is the movie I've been searching for

I'm glad I could help. :)