Is it normal for 5 y/o cousins to lick each other!?

[ALM25]

I am a single mother with a five year old son. A few months ago my son and his best friend who is also his five y/o cousin were in the bathtub playing. They got out to get dressed and I walked in to help them when I caught my naked son sitting on his cousins head, not his face. I asked what was going on and my son replied that they were playing a game. I asked several open ended questions and found out that they had also kissed each other's butts while in the tub. I stayed calm and explained that privates were only for you and not to touch others. I know that was normal, age-appropiate curiosity so I brushed it off. I no longer allow them in the tub or bathroom together. Last night I caught my son under the covers with his cousin, I again calmly asked my son what was going on and he immediately told me that he was licking his cousin's penis. Upon further investigation he confided that this happened several times. He asks his cousin to lick his penis and the cousin sometimes will do it. I asked what happens if the cousin says no and he looked at me like, "Duh, mom" and he said that if either says no then they don't do it. He told me he saw it on a sex movie and wanted to try it. He was very forthcoming and wasn't shameful about it or scared he was going to get it in trouble. I have no idea what movie my son saw or where he got that idea. I'm just worried because this is the second incident and I do believe my son was the  
instigator

[Kevin Kennedy, Ph.D.]

No, the behavior is not normal. Children do not spontaneously engage in this kind of behavior. Your son's explanation is plausible - i.e., that he viewed some sexual interactions and is mimicking those behaviors. Now of course this invites the question of where he would have viewed such behavior and this demands additonal conversation with him. The behavior is worrisome but does not automatically indicate he was mistreated. More information is needed and hopefully he will provide it.

[ALM25]

My brother is unbelievably mad and upset and I know his feelings are justified. But he's making my son out to be a pervert. His son willingly participated from what I have gathered. I'm just worried because this happened a second time and from all my research this seems to be a red-flag. From the bottom of my heart I don't believe my son has ever been molested. I'm not aware of there every being a chance! I promised myself I would never be the parent who ignored these types of situations or swept them under the rug like they didn't happen. Does my son need to be evaluated? Is this normal?