I don't know if I actually believe this, but I've heard reports that cause me to assign a non-neglible probability on the chance that sexual relations with between children and adults sometimes don't cause harm. For instance, see the Rind et al. report:
..."Child Sexual Abuse does not cause intense harm on a pervasive basis regardless of gender." Simplified, Rind et al. (1998) found that 3 out of every 100 individuals in a CSA population had clinically significant problems (compared to 2 out of every 100 in a general population).
Rind et al. contended that the