In general, I do not think that juveniles should be tried as adults. We assume that juveniles are too young to do a variety of things -- drink alcohol, smoke cigarettes, drive cars, vote, have sex with adults, sign contracts, give themselves permission to participate in school sports. Given this, we obviously believe that they are not capable of making rational decisions in a number of areas. So why, then, do we assume that they are capable of making decisions just like adult decisions when it comes to crime?
I can definitely see why people would want to charge juveniles as adults when they commit crimes, especially bad crimes. But it does not make sense given what we assume about their mental and emotional states.