S.L.
I've had a few hundred 4 year old's in my daycare through the years plus my own 4 daughters. 4 year old's lie. If anyone thinks theirs doesn't, then they are really good at it LOL! It's just the age that it starts. Eventually, they grow out of it. I wouldn't put too much emphasis on it yet. Just talk a lot (often, not lecture) about the importants of knowing between truth and lie, fact, fiction, right, wrong, etc. They may know it's not true. But they don't yet fully understand why it's wrong. It's also a good time to read them stories like, "The boy that cried wolf".