My son had ADHD as a child. So did my sister. We wished they would lie! They were so bluntly honest all the time it was embarrassing. I used to lie a lot as a kid. Mostly out of fear and self-preservation. We got no brownie points for telling the truth as kids. It was a beating either way, so might as well try to lie and get out of it! As soon as I got away from my parents, I stopped lying. Go figure.
There are lots of reasons people lie, fear, attention, low self-esteem, immaturity. I think when the reason goes away, the lying will often stop.
Cog