Talking about nudity, all i can say is that children have no problem with it because they are pure and inocent, if nudity would be that bad than children wouldn't born naked.
About sex, i also have seen on documenteries that primmates use it to streighten the "tribe's" affection per each others.

Ayman

Only God Can Judge Me
الله فقط يمكنه محاكمتي

I am you and you are me, if you love i love, if you suffer i suffer
أنا أنت, و أنت أنا, إذا أحببت نفسك أحببت نفسي, إذا عانيتَ عانيتُ