Friends are not only for people. Female baboons form close bonds with other females in their troop. Babies show signs of being picky about who they spend time with. They know faces they have seen. A baby can also react when another child is upset.

At first, very young kids play near each other. They do not do much together. Then they learn to talk, and their play changes. Some kids who are not yet in school have one special friend. Groups of friends can start to form too.

These kids often like to play with kids of the same gender. Gender means being a girl or a boy. Friendships are more common between kids who like the same things. Both of these ideas are about who becomes friends.

Kids in school learn what to do when friends do not agree. Making a friend also takes time together. In one study, it took about 50 hours together to go from knowing someone a little to being a casual friend. That is how long it took.

Words to know

• baboons: kind of animal
• troop: animal group
• gender: girl or boy
• casual: not very close