What could cause enlarged prostate common in young boys?

Not aware of any: I suppose a kid can get an infection in his prostate(which might enlarge it), i'm not aware of condition affecting pre-pubertal males nor do I recall ever having read of one. A narrowed tract (xray) going through the area of the prostate in kids is more likely an abnormality of the pee channel, not enlargement of the prostate as would be seen in adults.