I cannot think of any official form where I have to list my children's date of birth and address, So conversely can see no way they can be on a database for the use of train inspectors. I doubt that even the police have any more than a partial picture of children and who lives where and their ages.
Based on previous discussions on here, regarding crime and punishment. I think you will garner little sympathy.
I am interested in what database they checked, and who they are? I doubt that a 16 year old is on any database a ticket collector can check, I reckon your son was bluffed into...