We are discussing the use of the word "terrorism", not the word "terror". Terrorism is a political philosophy which aims to use "terror" to achieve political aims. It seems to me more likely that the groups of youths (or others) in question are more likely doing this for amusement, and not for political aims. Therefore, whatever else it is, it is not terrorism.
Derailing a train and causing hundreds of deaths doesn't count as terror because there was no political movement behind it
