DELAND, Fla. - A grand jury indicted four Florida teen-agers yesterday in the shooting death of a Canadian teen-ager who was on spring break in Daytona Beach.

Mark Fyke, 18, was talking with his mother in Canada when the youths walked up and demanded money on March 15, police said. He was told to hang up - and then fatally shot in the head with a .38 caliber revolver.

''He was telling me what a good time he was having ... moments later, in an instant, my whole world was turned upside down,'' his tearful mother, Christine Fyke, said after the judge and jury left the courtroom.

John O'Neal Rainey, 17, of Umatilla, was charged with first-degree murder and attempted armed robbery with a firearm. Donald William Shoup, Jr., 18, of Holly Hill, was charged with being a principal to first-degree murder and attempted armed robbery with a firearm.

Sealed indictments also were returned against two 15-year-olds: Scott Russell Malone of Umatilla and William Marshall Schmidt of Astor. Malone turned himself in last night and Schmidt was picked up at a friend's house a short time later, said Daytona Beach police department spokesman Al Tolley.