What punishement can minors get?

The fact is they are children themselves. Children over the age of 10 can be tried for crimes in England, and if their crime would have carried a life sentence for an adult, it can also carry a period of "indeterminate" detention for a child. This is in effect a life sentence, since the option of a life sentence is not open to judges sentencing children. Shooting them may be a popular option, but most civilised people would not want to condemn someone forever for something they did at the age 10, no matter how bad it was. They need an education, and we need to be satisfied they are no longer a danger to the public and can lead normal, productive lives before they are ever released.