a harsh sentence can be given out with an assault charge. you cant just decide to charge someone with something that carries that harshest penalty simply to make a point. you make charges based on what you can prove, not the punishment you want them to receive. You also don't know the details of the fight. what if he was knocked unconcious from hitting his head on pavement (and this actually happened to me. I received a concussion and was knocked out in a fight after I got slammed down on the ground. the punches and kicking wasnt what did it)
regardless, charging them as adults is just a punitive measure. it doesnt actually reinforce that what they did was wrong, it simply puts a felony on their record which will make them essentially useless in their adult life. felons can make something of themselves but it isnt likely.