In HCI, adult concerns about technologies for children have been studied extensively. However, less is known about what children themselves find concerning in everyday technologies. We examine children's technology-related fears by probing their use of the colloquial term "creepy." To understand children's perceptions of "creepy technologies," we conducted four participatory design sessions with children (ages 7 - 11) to design and evaluate creepy technologies, followed by interviews with the same children. We found that children's fear reactions emphasized physical harm and threats to their relationships (particularly with attachment figures). The creepy signals from technology the children described include: deception, lack of control, mimicry, ominous physical appearance, and unpredictability. Children acknowledged trusted adults will mediate the relationship between creepy technology signals and fear responses. Our work contributes a close examination of what children mean when they say a technology is "creepy." By treating these concerns as principal design considerations, developers can build systems that are more transparent about the risks they produce and more sensitive to the fears they may unintentionally raise.