At some point most children dream about being their favourite movie character.     Children everywhere get the chance in the back yard to be Luke Skywalker, Superman or Lara Tomb Raider.     But not many get the opportunity to be their movie hero in front of 2000 people.     That is exactly what faces seven-year-old Thomas Lacey.     Thomas, of Warrandyte South, was this week chosen to play the part of young Cosmo Brown in the Melbourne production of Singin' in the Rain.     The part, made famous by Donald O'Connor in the 1952 movie just happens to be his favourite character.     "He loves the movie and watches it all the time and he loves the Cosmo Brown part because he is the funny one," his mother, Julie, said.     Thomas already had five years of singing and dancing under his belt.     He sings on Tuesday nights, has a dance class on Wednesdays and spends all day Saturday in various classes.     "When he is not in a class he sings and dances all over the house.  He loves it," Ms Lacey said.     Thomas is excited by his new part.     "I am really looking forward to the show," he said, "But on opening night I will be really, really, really nervous."     The Melbourne season opens on October 5 at the Regent Theatre.