Have you ever noticed that a kid punches another little one for toppling a Lego tower? Such revenging approach is quite common among kids. But when a kid helps another, that kid may not say "thank you" to the person who helps him or her without being taught. Why?

A recent study suggests that for children, retribution may come before gratitude.
About the study
In the study, the researchers recruited 330 children between the ages of 4 and 8 to participate in a series of experiments examining if they will punish the person who wrongs them and pay back the person who helps them.

In the first phase of the game, a child was invited to play a computer game with four other "virtual players" controlled by the researchers. The four other players each received a sticker, but the child got none. Then one player (randomly selected by the researchers) "chose" to give a sticker to the child. Next, the child who received the sticker could give it to a player freely.
In the second phase of the game, one of the other players stole a sticker from the child, and then the child could steal a sticker from another player.
It turned out that kids, even the youngest ones, readily took revenge on the sticker thieves when they could take back a sticker. But they didn't tend to give the sticker to the one who gave them the sticker before.

Immediately after each game, researchers asked the children about the identities of the givers and takers, and the kids could recall both groups with high rates of accuracy.
These findings showed that the kids punished the thieves on purpose while they might not repay a kind deed.
What parents should know

The researchers believe that revenge is more of a defensive move — protecting oneself from future victimization. "Kids aren't out to get people," said Peter Blake, the lead researcher. "They're sending a signal to the person, but also to the broader world that 'I'm not a sucker.'"
In addition, parents needn't be troubled by the findings. It just seems that retribution may come before gratitude. If you want to teach your kids gratitude, you can tell them a considerate bedtime story every day.
In the final trial of the experiment, the researchers told children a simple story illustrating gratitude between peers. The result showed that they were more likely to pay back their benefactors after hearing the story.