Early adolescent boy exposure

My nephew just turned 14.  He is a good kid for the most part.  He is just somewhat pesty as boys can be.  He was having a sleepover with my other nephew who is 10.  The two are close and enjoy playing sports together.  The 14 year old was going to take a shower and called down to the 10 year old to come upstairs.  The 10 year old replied, "no! I know your going to do something inappropriate."  The 10 year old's mother, my sister, asked what was meant by that comment and the 10 year old didn't give her an answer.  After the two boys were separated, my sister asked her 10 year old son what he meant.  He said that the 14 year old showed him his penis when ever they have sleepovers and he began crying, I think upset because he was afraid that the 14 year old would get in trouble.  When asked how long this has been going on the 10 year old replied, "I don't know, how long have we been having sleepovers?"  

My sister called me with this wondering how to handle it.  Should she tell our other sister who is the mother of the 14 year old with the risk of jeopardizing their relationship?  We're pretty sure that this is abnormal behavior and are wondering how to handle it.  Any advice and insight into this type of behavior would be appreciated.

Thanks

[Kevin Kennedy, Ph.D.]

The behavior does invite concern, and you should communicate this to your sister. Think of yourself in the same situation. You would want to know, otherwise you would not be in a position to get help for the child.