Spielberg, who had worked with a very young actor (Carey Guffey) on Close Encounters of the Third Kind, felt adequately prepared to work with a cast of children. Six-year-old Drew Barrymore, born into the famed Barrymore acting family, was the first of the three to be cast — the director loved her energy and was particularly charmed by her claim that she was the drummer in a punk band called the Purple People Eaters. Robert MacNaughton, who played Elliott’s older brother Michael, auditioned eight times before landing the part.
Spielberg and his casting people had seen hundreds of boys hoping to play the central role of Elliott before he met with Henry Thomas, a shy 10-year-old from Texas. Thomas, a big fan of Raiders of the Lost Ark, arrived at the audition wearing a small bullwhip on his belt. His initial reading failed to impress, but he was given an opportunity to do an improvised scene in which he was supposed to hide an alien friend from a government agent who knocks on his front door. That reading — and his realistic tears (brought on by thoughts of his dead dog) — moved Spielberg, whose enthusiastic (and relieved) “O.K., kid, ya got the job!” can be heard on the audition tape.(TIME magazine: Steven Spielberg, the Prince of Hollywood)