This study investigated the influence of question format on preschool-aged children’s errors, their response accuracy, and their tendency to say “I don’t know” when given non-misleading questions in a neutral, unbiased context. Children (3 to 5 years old) participated in a craft-making session that included a staged “accident” with two experimenters differing in gender and appearance; the environment also had several distinctive features. One week later children were interviewed about actions, participants, and environment; questions were yes/no format with the veridical response “yes” (“yes” questions), yes/no format with the veridical response “no” (“no” questions), and specific wh- format questions. Question format substantially influenced children’s responses: they were most likely to make errors if asked “no” questions, and were unlikely to answer either yes/no question with “I don’t know.” In contrast, children spontaneously and frequently said “I don’t know” to wh- questions about content they did not recall (environment), but not about content that was well recalled (actions.). Implications of question format for reliability of eyewitness testimony by preschoolers are discussed.