What if it wasn't a diaper rash, but a clear hand-shaped bruise on the child's upper arm or back or rear end? Would you wait to call CPS and talk to the parents first? Or would you call immediately? We are mandated reporters--we are supposed to call CPS for even suspicions of abuse. That doesn't mean a clear pattern--abuse doesn't have to have a pattern to be wrong. ONCE is wrong.

And especially in the case of something like this, you don't even want to THINK that your delay in calling might mean it might happen again. I've never seen or heard of a diaper rash that looked bruised and was as localized as the OP described. A bleeding rash is one thing, those can happen pretty suddenly sometimes, but bruised? Not so much. Bruises require trauma. And if something happened that might have been traumatic to that area (say, an older child falling on something) then the father REALLY should have offered up an explanation instead of "she has a rash, there's cream" and zooming out asap.