One of the two 15-year-olds hit by the ICE train on a bridge near Rathenow in Brandenburg was killed, while his friend suffered severe injuries, police reported.
Authorities reported finding spray paint and other graffiti utensils at the accident scene.
Passengers on the train, which was on its way to Interlaken, Switzerland from Berlin, were forced to disembark and take buses to Hannover and Braunschweig. Train service in the area was delayed heavily until midday when authorities reopened the line.
The tragedy occurred just one day after three children in Cologne were severely injured while playing in a Zollstock district train yard.
An 11-year-old girl and a 12-year-old boy were flown to a special clinic with severe burns, while another 12-year-old girl was taken to a nearby facility, police said late on Thursday.
The three children and several of their friends had been playing at the yard near Neuer Weyerstrasserweg on Thursday afternoon.
They climbed onto a parked train car near aerial contact lines, which at some point released a massive electrical charge and electrocuted the trio.
A nearby resident discovered what had happened and called police after hearing a loud crack around 5:10 pm.