A movie in which two teen age neighbour kids along with their yonger bro...
Become small... the girl gets angrey with boy... they all are so small they all land up in a ceral bowl
They scream 4help...

I believe the movie you are looking for is Honey, I shrunk the Kids: Honey, I Shrunk the Kids (1989) - IMDb (http://www.imdb.com/title/tt0097523/?ref_=sr_2)