The British actor was given an unflattering makeover for his part in period drama Anna Karenina and his children were so horrified, they asked him not to meet them in front of their friends.
Law tells Britain's The People newspaper, "My kids banned me from collecting them from school unless I was wearing a hat and hid."
The Alfie star also reveals his eldest son, Rafferty, 15, has been teaching him street slang in a bid to make his dad cool.
He adds, "My oldest, Rafferty, who's almost 16, has been teaching me some London street slang because he wants me to be a bit cooler. At the moment he thinks I'm really uncool... It's utterly bizarre. It's like a new language. I sound b**ody ridiculous saying it so I've decided to stop."