Very small children are brutally honest. Show them a picture you've painted, sing them a song you wrote: If they don't like it, they have no problem telling you that you suck.

So when precisely does the ability to disguise one's opinion emerge -- to engage in what psychologists call "ingratiation behaviort", and lie and say that you're impressed when you're not? I was surprised to learn that researchers haven't looked too closely at the beginnings of flattery. Apparently the first studies have recently been done by KangLee at the Ontario Institute for Studies in Education. As the University of Toronto Magazine reports:

They asked a group of preschool children ages 3 to 6 to rate drawings by children and adults they knew, as well as strangers. The preschoolers judged the artwork both when the artist was present, and when he or she was absent. The three-year-olds were completely honest, and remained consistent in their ratings; it didn't matter who drew it, or whether the person was in the room. Five- and six-year-olds gave more flattering ratings when the artist was in front of them. They flattered both strangers and those they knew (although familiar people got a higher dose of praise). Among the four-year-olds, half the group displayed flattery while the other half did not. This supports the idea that age four is a key transitional period in children's social understanding of the world.

There are, Lee says, two reasons to flatter: Either to reward someone's behavior, or to butter them up in case you need them to be nice to you later on. Lee's not sure which strategy the four-year-olds are pursuing. But because they flattered strangers as well as people they knew suggests "they are thinking ahead, they are making these little social investments for future benefits."