Parents of 3 to 5 year olds often get concerned when their child lies. One more fun fact for preschool parents is that this is the age when children start this important mental development. Lying is truly a growth milestone so don't fear lying, just be aware that its happening and it is an important development.
So what's happening? Your child is figuring out that other people perceive things differently than she or he does. “I thought the cookie was for me, but I don’t think Mom did so I’ll tell her the dog ate it.” No one wants to encourage unwanted behavior, but lying is an important mental development and not a sign of a “bad” child. It is normal and should be corrected in a calm manner.
Feel free to tell your child you know the dog didn’t eat the cookie, but unless you notice your child becoming a habitual liar, it is usually not a problem. Its just a growth stage like learning to walk. Here are two links that might be helpful…
The first is one of my favorite science sources…a good read but long. The second link is a bit more practical. Good to read both.