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It’s both a scientific mystery and a parenting conundrum: how do children learn to share?

Children as young as three understand the concept of fairness. Fair means one child should get the same number of stickers as another. But put a young child in charge, and fairness seems to go out the window; young children tend to hoard when they are the ones who are deciding how much of their own candy or toys to hand over.

New research is beginning to untangle the disconnect between knowledge and behavior, with a surprising finding: Young children asked to predict how they will divvy up stickers already anticipate they will tip the scale in their favor. When it comes to sharing, the three- to six-year-old set is — scientifically speaking — a bunch of self-aware hypocrites.


“They were surprisingly honest and self-aware. They said, ‘I realize I would keep more for myself,’ ” said Peter Blake, an assistant professor of psychology at Boston University and a co-author of the work. “Anything that involves giving up resources brings us into an evolutionary context, where kids might have a bias to be more self-interested” in order to survive to reproduce.

The study, published Wednesday in PLoS ONE by Blake and colleagues from Harvard University and the University of Michigan, recruited participants from visitors to the Museum of Science in Boston.

First, researchers gave each of the children four stickers with carefully researched qualities that would be desirable to children ranging from three to eight years old: their favorite color, smiley-faced, scratch-and-sniff. These stickers belong to you now, the researchers told the kids.

Then, they asked them to divide up the stickers, to share them with another boy or girl. Next, they asked the children how many of the stickers another boy or girl should share.


Children of all ages agreed that other children should split up the stickers evenly. But when it came to their own sharing, younger children were far more likely to keep more for themselves. To test whether this was a problem of impulse control, the researchers ran the children through a gauntlet of tests designed to probe how well they could inhibit impulses, seeing whether they could, for example, view a picture of the sun and say the opposite word, night, in a short timeframe. The ability to inhibit their first impulses seemed to have nothing to do with their decision to keep more stickers.

The biggest difference that did emerge was how children spoke about why they or another child shared stickers. The youngest kids talked far less often about sharing being fair as the reason for a decision to share, and far more often about their own desires.

In a second experiment, researchers changed the question slightly. They asked another gorup of children to imagine how many stickers they would give to another child. Despite the fact that children of all ages had made it clear that they understood equally that splitting the stickers was fair, the youngest ones predicted they would hoard them -- which is precisely what their peers had done in the first experiment.

It wasn’t a matter of trying to do the right thing and failing; those kids knew what they wanted. Stickers.

Now, Blake would like to test the behavior more broadly, in children from different cultures. He wonders whether in societies that place responsibilities on children earlier, young children start acting fair earlier.


He’s interested in understanding the cognitive processes, the mental machinery, that underlies behavior. But he says there may be a practical application, too. Understanding the behavior could provide an opportunity to use such understanding to improve behavior or education -- by finding ways to teach kids to share more effectively at a younger age.

After the sessions at the Museum of Science, “the parents seem relieved, to some extent,” Blake said. “They say, ‘I’m glad that they know what the right response is, but how can I get them to be more fair?’ ”

Carolyn Y. Johnson can be reached at cjohnson@globe.com. Follow her on Twitter @carolynyjohnson.