Modeling behavior for a child
As it is, the example set for the boy is that you can make friends and influence people by lying about the most obvious thing rather than looking for something you can truthfully point to as positive.
It's actually a very bad example to set for a child that lying is the way to achieve one's goals, for the end justifies the means. There's a famous Talmudic (Yevamos 63a) account of a clever child who figured out a solution to the problem of his mother always making the opposite of what his father, Rav, requested for dinner. He switched the dish when conveying the rewquest to his mother. His father noticed the change and rmarked on it to his son who then proudly revealed his strategy.
Rav ordered him to cease and desist. "Do not do this," he said, "so you will not learn to lie." Not willing to compromise on the truth -- even for the sake enhanced harmony-- was a powerful lesson for a child. And that child grew up to be Rav Chisda.
Now to connect the point of the previous two paragraphs: let's look at what Aharon HaKohen was famous for. Chazal say that all the Jews mourned him -- even more than Moshe -- because he was an ohev shalom verodef shalom [a lover and pursuer and peace]. He excelled at reconciling people who had a falling out. How would he do it? He'd go over to each person and tell him/her that the other wanted to make up. But, here's the big difference between a great man and the one shown in the cartoon: he wasn't lying. He had the ability to recognize the part of the person that really did want to make up. That's what he brought out in people. And that's how he proved so successful in bringing about peace.
PS A few weeks after I first posted this, I read R' Dr. Abraham Twersky's book, Life's Too Short! St Martin's Press, 1995). On p. 158, he addresses this exact point of building self-esteem without resorting to lies, particularly in a relationship with a child. He recounts his thoughtful response to his 7-year-old grandson's violin playing:
Although the melody was grossly off tune, I was about to say, "That was beautiful. I'm really proud of you. I caught myself, because it was not beautiful, and to say so would have been a lie. Instead I said, "I know that tune. Let's have a concert. You play and I'll sing it." We did so, and that child beamed with pride. I had acknowledged his playing a melody that I could recognize, and I had not lied to him.
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