Children from less privileged families are more likely to behave altruistically than their wealthier counterparts, according to a study of 74 pre-kindergarten toddlers by the University of California, and published in Psychological Science.

In the experiment, researchers played with children one by one for two hours and told them that they had earned 20 tokens. At the end, they could trade them for “a really great prize.”

The toddlers, who were an average of 4, were then given the opportunity to donate some or all of their tokens to “sick children” who weren’t able to come to the lab. More than a half of them chose to donate at least one token, and 34 children did not donate.

The researchers kept track of the children’s family income, and they found that each increase of $15,000 in income carried a reduction of about two fewer tokens donated, Jonas G. Miller, a co-author of the study, explained to Quartz.

The researchers also found some indication that the more altruistic children are likely to be healthier, too. Electrocardiographic data that researchers gathered through electrodes showed that those children who had given their tokens away had a greater level of vagal flexibility right afterwards. This indicator is linked to health outcomes, including decreased risk for heart disease, hypertension, and diabetes, Miller said.

“Higher vagal tone has also been associated with a number of positive social behaviors and emotions in children and adults, like being more prone to positive feelings, less anxiety and depression, and less acting out and aggression,” said Miller.

Both Miller and a group of Harvard researchers who recently looked at kindness in children say the recipe for raising more altruistic children requires that parents nurture those qualities. But even if being generous is healthy for our children, it appears many US children aren’t getting that training.

The Harvard study of 10,000 middle and high schools students found out that almost 80% said that their parents taught them that personal happiness is more important than caring for other people.

“Children learn a lot through observation and imitation of adults,” said Miller. “Parents that model kindness in their daily lives may set a good example for their children.”