In two experiments, we investigated whether imposing a secondary task is an effective technique for detecting child deceit. First, 85 children aged 8 to 11 years old provided either a true or false report of a recent school event. At interview, some children were asked to gaze towards either the interviewer's face (IF) or a teddy bear's face (TF), whereas some children were given no gaze instruction. In both the IF and TF conditions, lie-tellers provided significantly fewer details than truth-tellers. A total of 192 adult evaluators then judged the credibility of 10 children's reports from one of the three ‘gaze’ conditions with and without guidance on level of detail. Evaluators discriminated truths from lies successfully when judging children instructed to look at IF, but not when children were asked to gaze towards TF. Evaluators who received guidance demonstrated better discrimination between true and false reports than evaluators who received no such information.