Network Rail has released what the track operator called "shocking images" of young people taking risks on Sussex's railway lines.
The company said the images had been gathered on tracks between Horsham and Crawley in May.
Both incidents happened earlier this spring as lockdown restrictions were eased and both took place on level crossings covered by CCTV cameras.
The first incident occurred on 4th May at around 5pm, when two young girls were seen lying down on the track at a crossing near Horsham.
In the other, which happened on 14th May, two boys were spotted walking down the track at Bewbush near Ifield.
The incidents came after figures released in March showed there was a shocking 40% increase in youth trespass incidents in South East London, Surrey and Sussex after the region emerged from the first national lockdown.
Network Rail said the pictures had been released to remind young people and their parents that their actions can have serious consequences and put the welfare of passengers at risk too.
The children whose identities have been disguised have been spoken to by Transport police officers.
Network Rail's head of route quality, health, safety and environment, Vincent van der Hoeven, said:
“We really must get the message across to children and their parents the dangers of trespassing on the track.
“We are putting efforts into getting the message across in schools and on social media through our ‘Parallel Lines’ film and ‘You vs Train’ campaign.”
Nicola Dooris, community safety manager on the South East Route, added:
“Unfortunately during lockdown, we have seen an increase in the numbers of young people messing about on the railway.
“On that section of track trains often travel at 85 mph and at that speed, unlike cars, trains can take hundreds of metres to stop, a fact many young people don’t realise.
“Using CCTV like this I’m often able to track down young people and talk to them and I’d much rather do that than help our staff cope with the aftermath of young people being killed.”
Network Rail has also worked with British Transport Police on the tough "You vs Train" campaign for three years, aiming to educate young people on the devastating and wide-reaching consequences of trespass.
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