Why are young children particularly prone to make false positive errors or false alarms when identifying a wrongdoer? In three studies, the problem was approached using a signal detection analysis, focusing on the moral costs of false alarms, as understood at different points in development. The findings are as follows: (i) decisional criteria became more conservative, indicating fewer false alarms, with age in three studies; (ii) children's beliefs about the seriousness of false alarms and misses changed from (a) a non-moral concern to (b) a moral concern for misses to (c) a moral concern for false alarms. (iii) These findings were replicated in two demographically different communities. More critically, (iv) framing of the filmed event, for example, as a moral transgression (stealing) or a pro-social (helping) act (Study 1) and as intentional with little damage or unintentional with major damage (Study 3), interacts with age in influencing decisional criteria. Copyright © 2012 John Wiley & Sons, Ltd.