Also isn't it true that if you commit a serious enough crime as a child that as soon as you get out of Juvenile Hall you get put on trial as an adult for it?
I don't think so but that will depend on the country. Probably the most serious one in the UK was the murder of James Bulger (a 3 year old) by two 10 year olds. Both were found guilty of abduction and murder, and imprisoned until they reached adulthood. Both were then released on parole, with new identities, and under what is known as a lifelong licence. A lifelong licence is a condition of the parole where if they broke the conditions of their release, or are found to be a danger to the public, can be immediately returned to prison for an indefinite period under the terms of this licence.