I'd like to know more about the situation but the person absolutely not at fault here is the mum and kids....they did nothing wrong.
Train companies over booking
Not enough trains and carriages
Strikes
People sitting in reserved seats (and refusing to move)
People not giving up seats for older people who need them.
I could understand if they got on a packed train and those seats were free you sit there until someone asks you to move. Sometimes people don't turn up
But if the train was full someone closer exit in an accessible seat could have given up their seats for the OAPs