Researchers have studied how young children share stickers. In one study, preschool children shared more stickers with a friend than with other children. Preschoolers were more willing to share with a child they did not know than with one they knew but did not like. In sticker studies, fairness was not the main reason preschool children shared. The giver's relationship with the other child mattered more. Sharing is hard for preschoolers, and arguments are common but usually short.

Babies and toddlers can react when another child is upset. Babies respond to familiar faces and show signs of being selective about who they spend time with. Infants as young as nine months old prefer individuals who are nice to people like them. Three- and four-year-olds tend to assume that people are friends if they see them share or help. Many preschoolers describe friends as people who love or care about each other.

Play changes as children grow. At first, toddlers play near other toddlers without interacting much. As they learn language, their play becomes more interactive. Young children spend most of the time they are with friends in pretend, imaginative play. Preschoolers may start to play structured games that involve rules and responsibilities. Friendships are more common between children who have similar interests, and preschoolers often prefer to play with children of the same gender.

Making a friend takes time together. In one study, it took roughly 50 hours together to move from acquaintance to casual friend. It took about 90 hours together to move from casual friend to friend. A close friend takes more than 200 hours of time together, according to one study of adults. Some adults reported spending hundreds of hours with coworkers but still called them acquaintances. How people spend their time and what they talk about affects how close they become.

Preschoolers may have one particular friend, and groups of friends can start to form. As children grow, they become more understanding of the differences between themselves and their friends. School-age children learn to deal with disagreements with friends. Older school-age children start to form lasting, supportive friendships. By about age 12, children understand that trust and support are the bedrock of a quality friendship.

Friendship shows up beyond people too. Female baboons form close bonds with other females in their troop. Baby baboons were more likely to survive when their mothers had close friendships with other female baboons. For female baboons, the quality and stability of relationships matter more than the number of them. As of May 2026, researchers report that as chimpanzees get older, they become more selective about the partners they spend time with, much as aging people do.

Back to the stickers. In a sticker study, preschoolers gave most stickers to a friend even when the friend had 100 stickers and a child they knew but did not like had only three. Preschoolers will give more to a wealthy friend than to a needy stranger, at least when wealth is measured in stickers. The 5- and 6-year-olds counted friendship for more than the 3- and 4-year-olds did, so social relationships matter more as children get older.

Words to know

• acquaintance: someone you know
• preschoolers: children before school
• imaginative: full of make-believe
• bedrock: solid base
• selective: choosy