A 14-year-old boy in Beloit, Wis., went on trial on juvenile delinquency charges in the July 26 slaying of a 9-year-old who refused to share his bicycle, and jurors were asked whether they doubted that a person so young could commit murder. None responded when Dist. Atty. James Daley asked the question during jury selection for the trial of the oldest of the three youngsters accused of beating and stabbing Anthony Darnell Wilson. The other two defendants are a 12-year-old boy and an 11-year-old girl. All three children have pleaded innocent and will not be tried under adult laws.