In the context of exposing minors to sexual acts it should also be noted that various elements of sexuality has changed significantly over time. For starters, "being of age" was often connected to reaching puberty and up until the mid 19th century ages of consent from 10-13 were deemed acceptable. It would be interesting to see how perception of actual sexual acts may or may not have changed.

 

Another thing from the view of actors is that performing sexual acts also carries a certain vulnerability (similar to birth or defecation) so a taboo can also have arisen from the actors rather than from the observer side.

This is particularly not true in the case of horses. About 8 days after giving birth to a foal a mare returns to heat and will mate with a stallion. The foal is most upset with what is going on and sees it all. I know this for it happen on my farmlet within the last month.

See https://www.youtube.com/watch?v=oxX1J7CHEN8 as another example.

 

ok thanks I didnt know that.