What kinds of things does someone have to see to lose innocence?

sex or acts of extreme violence, but this depends on your country's laws on innocence and your particular's area's view on innocence and how it is lost. I assume your country applies to the western view of innocence. If so, the answer given should suffice

Explanation:

Seeing sexual intercourse at a young age is seen in western cultures as loosing innocence, because you are introduced to the acts of pleasure (or reproduction) from an age that you are not expected to do so. Sex in itself can be weaponized and used to hold power over someone and take away theirs.

It is also thought that seeing acts of extreme violence also make you loose said innocence, because you are introduced to grotesque ways of behaving that could influence how you interact with the world in respect of empathy and your actions.