Maybe it's time for his parents to have a open, and honest discussion about the consequences of lying to people in genaral.
Look I'm not a parent, but I think the parents could sit him down and have him watch a cartoon movie or a documentary that gives good examples of what will happen when you lie. It has to be kind of educational, but shocking and scary at the same time. Or maybe they could have him read a comic book about why it's better to be honest instead of being a lier. Something on the lines of showing how honest people are able to gain people's trust easily and have people to call on when they need them themost vs a lier who people will always doubt and steer clear from even when the lier needs actual help in real life situations.
Look I'm not a parent, but I think the parents could sit him down and have him watch a cartoon movie or a documentary that gives good examples of what will happen when you lie. It has to be kind of educational, but shocking and scary at the same time. Or maybe they could have him read a comic book about why it's better to be honest instead of being a lier. Something on the lines of showing how honest people are able to gain people's trust easily and have people to call on when they need them themost vs a lier who people will always doubt and steer clear from even when the lier needs actual help in real life situations.