Usually when we think of lying, we think of words that are untruthful. Of course, there's some of that in The Witches, but the witches themselves are constantly deceiving through another means: disguise. The only way witches are able to pass for humans and trick children is because they are constantly in disguise – wigs, gloves, and sometimes masks – to make them look like normal ladies. They're pretty much telling everyone around them that they're someone they're not. If that's not a lie, what is?
Come on, everyone lies. The witches might be evil in other ways, but we can't blame them for their deception.
Storytelling itself is a form of deception.