"That's not fair." Maybe you have said it, or maybe you have heard someone else say it. Young children often protest this way. Even very young children understand what is fair. So what makes something fair? Let's look at sharing, cake, coins, votes and games to find out. Here is a question to keep in mind: what do people do when something has to be split? Let's start with sharing, which every child has to learn.

Here is the first thing to know about sharing: learning to share takes time. Toddlers, who are children under 3, are often reluctant to share, and they do not yet understand what sharing means. Babies seem to notice unfair sharing, though, because they look longer at unfair outcomes. Children often get better at sharing around age seven or eight. Where does the learning happen? Read on.

Children learn to share and take turns by playing with other children. Taking turns is one way to share. Each person gets a go, one after the other. Playing simple board games or card games helps children practice following rules and taking turns. When two children share a toy, each gets an equal turn, and setting a timer can show when a turn is over. A child can keep a few special things just for themselves. A child does not have to share everything.

Here is an old way to split a cake. It is called "I cut, you choose." It is a standard way for two people to split a cake. First, the person who cuts makes two pieces they think are equal. Then the other person picks the slice they like best, so neither person envies the other. That means neither one wishes for the other person's slice. Look closely at the cake, though. Cake is not the same all the way through, so two pieces of the same size can be worth different amounts to different people.

Before a game, someone has to go first. In soccer and in the NFL, the referee flips a coin before the game to decide who gets the first choice. Part of being fair is following the rules. In sports, fair play is usually thought of as following the rules. Fair play includes respecting the referee, the person who runs the game. Fair play is also deeply rooted in the Olympic ideal. It sits at the heart of sports ethics.

Now think about rewards, for work that people do. Here is a question: what if one person worked harder? Young children understand that someone who worked harder may deserve more reward. Young children also often prefer to hand out rewards equally, even when one person worked harder. Children expect people who do equal work to share the reward equally. Children will sometimes give up their own reward to keep things even with another child.

Studies done in many different places found that children dislike getting less than another child. In a study of seven societies, children in every one would give up a food reward to stop a peer from getting more. That means children in all seven places were willing to give up the reward. Some parts of fairness look the same around the world, while others change with local customs.

Groups can also decide things by voting. In a majority vote, the choice with the most votes decides the outcome. After a vote, someone may be unhappy with the result, and that is part of voting. Here is one more fact, and it is about the law in this country. In the United States, trial by jury is a right guaranteed in the Constitution.

Words to know

• referee: game judge
• envies: wants theirs
• majority: most votes
• outcome: the result