While it is normal to be scared of things, some children are so scared that it disrupts their lives. This is called an anxiety disorder. To help children with anxiety disorders, we need to know how anxiety disorders start. From other research we knew that toddlers who avoid new situations are more likely to become anxious later in life. They are more likely, which does not mean they all become more anxious, just some of them. We wanted to know if brain activity could predict which children would become anxious. We studied avoidance in toddlers and invited them back as preteens. We studied their brains while they were resting and while they were making mistakes in front of somebody else. We found that brain responses to mistakes predicted which avoidant toddlers became very anxious as preteens. This helps us understand who might develop anxiety, so that we can help!