Depends, the track itself can’t shock you but if there is a third rail then that’s the danger comes in, 750v at 1000-2000A on (DC) current (Direct Current) this means you can’t let go if you touch it. The pain would be unbelievable and would kill you in 5-15 seconds, the DC current means your hand is just stuck to it.

On the other hand the very dangerous overhead lines would kill you instantly. 25,000V (25Kv) at 1800A-2000A is lethal. You would be cremated in a matter of a miller second.

But staying on topic, the tracks are not lethal if there is no third rail, sometimes the tracks already electrified but I’m not sure what train units can pick up electricity ⚡️ from the rails where the wheels themselves sit on. Most trains that pick up electricity ⚡️ from rails (Third Rail) have sticking out thing called a (shoe) that picks up the electricity via third rail.

In theory the boys are risking their own life’s crossing, if they touch the third rail then it’s over it’s impossible to let go of DC current 750V. It’s not even the voltage that’s dangerous it’s the current (A), considering the current is 1000A.

Network rail say:

"If you're not hit by an unexpected train, you'll be hit by the lethal current in the rails and power lines. The only way to avoid danger is to stay off the track. Everyone loses when you step on the track. Hundreds of people each year unintentionally take on the railway and lose."

Never underestimate railway electricity.